1) Use "hard polymer" for the miniatures. They would still be plastic and solid color, but they would sculpted out of a less breakable material similar to the Reaper bones (or Reaper Bones Black) miniatures. Not sure if this would eliminate the possibility of having "partially poseable" miniatures like we had in the old days (Gargoyle can turn his head or remove wings, Ogres can move their arms and heads, etc). If that "feature" can be retained, then go for it. Maybe with ball and socket joints? (use glue if you don't like it)
2) Use Quad fold board (Easier to store), with some kind of sealer on the "bare edges" for protection of course. As for making the squares bigger, it's not necessary to make them 1 inch, but at least 24mm to better fit the bases.
3) Dice can be wood, but they would have a clear coat of varnish to protect the ink on the images from wearing away. Inscribed plastic dice would be fine though, keeping the same overall style and colors. Some people say there should be more dice, but opinions vary. Should each person have their own dice, or just an extra set for Zargon? I don't mind passing dice (in pre-covid days), and you can use the cardboard trays (or plastic forms if your set came with them) for makeshift dice rolling boxes.
4) Equipment Deck would be included alongside the Armory board, with explanation that the number of cards don't limit the availability of equipment pieces. Include cards for Bracers, Spear, and Hand Axe. Cloak of Protection is a question... should there be a generic, buyable cloak that's equally strong to the Wizard's Cloak? I would be inclined to just leave it out of the NA set for this purpose. If it's a generic, more expensive piece of armor that ANY Hero can wear (but especially useful for the Wizard before finding the artifact) I could justify it. Wearing a cloak instead of other piece of armor helps a person with "pits of darkness" traps but these don't exist in these expansions yet.
5) Potions (could alternately be called "Alchemist Shop") deck. Even though it is small, having a card for each Potion for the two expansions would be neat. And yes, that means duplicates of the Treasure deck potions would appear here too. This doesn't limit potion availability. And still have a page in the quest books for the Alchemist Shops.
6) KK & ROTWL AND Dark Company included. Making room in the box with the quad board and the extra miniatures and such can fit in there. The new tiles would have the same quality (thickness, double sided where possible or just black finish on the reverse side or maybe a little icon on back signifying it is part of the expansion) as the GS tiles. New Artifact cards would be the same size and quality of the other Artifact cards.
7) Quest book would have a nice finished color cover (not just paper). Same with instruction manual.
8) Forms inside the box to store miniatures better, if space allows. And sturdier box, period. It's possible to make very sturdy cardboard boxes.
9) Body point counter for "big" monsters. Yes, not many of them in the first two expansions, but will help out later! But still keep the Skull tiles for nostalgia's sake or those 2 BP monsters.
10) Mercenary token/chits for each Hero (so you can more easily track who has what).
11) Search token/chits to more easily track who has searched what room for what, whether for use by Zargon or the Heroes.
12) Sturdier GM screen for Zargon (the classic one is great but starts to fall over as those cardboard tabs' creases get worn).
13) Include unique EU treasure cards in the Treasure deck, specially marked on the face side in case the GM wants to exclude them.
14) In the back of the rule book, include the 2nd Edition EU rules. Yes, both sets of rules in 1 book. Sort of like how back in the day electronics came with an instruction booklet that had it in four languages or whatever.

15) Clarify a few rules (insert here the stuff we debate about on the forums). Remove the "search for secret doors inside a pit" confusion.
16) Re-release ATOH, WOM, EQP and BQP. This would be the harder part, because it means a balanced version (an error corrected version of Phoenix) but especially solving the issues with EQP/BQP. Perhaps the two EU expansions could be combined and the two NA expansions could be combined so there's only two more boxes to buy. Give the new bad guys in the EU expansions their own monster cards. Add another body point counter (very useful for the NA expansions!). Re-scale the EQP/BQP miniatures to more closely resemble the proportions of the GS minis, otherwise they are fine.
17) Plastic coat the cards. I don't mean 100% plastic, but more "smooth" than they are now.
18) New Heroes. Add the Legacy of Sorasil extra Heroes. Male and female versions of all 8 extra Heroes with their own character boards. Maybe this would require its own set, as their could be new spell/skill cards to go along.
19) Release it to retail stores, and make it available in every country that originally sold HQ. This wouldn't be a one and done limited edition, but like a regular game out there for the masses.
20) Slightly larger character sheet, that includes the coat of arms thing for doodles, but all the other material from the NA and ADK character sheets. Tasks completed to include not just the 14 quests but quest pack quests as well.
20) Insert advert for an app (works with or without smart phone) that lets you subscribe and see everything. But if you pay a fee, you can download other people's quests and contribute your own (maybe free trial lets you do this too, but otherwise you can just view them, so you'd have to have it pulled up to play). Contents and giveaways for user contributed content, top quests, etc. Get the community involved. The app would also have an easy to use point and click Quest creator, similar to HeroScribe with the improvements we'd all like to see. But still include the blank map and symbols in the quest book like the classic version. Printable blanks on the web page too.
21) include those little pencils.
22) Include a little flier about painting your own miniatures (maybe post beginner paint guides on the website/app).
23) For furniture it's tempting to say "all plastic" but now the furniture will lack color, whereas before at least the cardboard portions had color to them. Maybe a basic paintjob on all plastic furniture? And I like the idea of pegs for removable parts (bottles, candlesticks, rats, skulls). When the pieces are polymer they're a lot more sturdy than before. If any extra would be included I would say there should be 1 extra treasure chest.
24) Doors that open (putting a little hinge on the doorway is a cool idea even if the door itself is too small to "really" allow a figure to pass through on its own without turning it into a huge, multi-square archway. Similar to the Zombicide black plague doors, but made out of polymer that's slightly flexible (instead of hard plastic that will show stress marks with too much use, bend and break). There would be 23 doors (the standard 21, plus two "special" doors for the iron and wood from KK/ROTWL).
25) For the collectors, release a "deluxe" edition that has metal miniatures (each primed in the same colors as the plastic editions, silver underneath), fancy dice (two sets, one for zargon with black/red and one for the heroes and translucent movement dice with gold chrome pips), maybe a velvet dice rolling box/casket, hologram foil cards? Maybe the board would be made out of several wood panels, with velvet on the edges, but the actual board image would be a matte finished laminated wood kind of thing, almost like you were playing on a picture frame, with the four sides connecting together, then fold back together for storage). What would the overall box be made out of? Maybe some kind of self contained chest made out of sturdy material, perhaps wood? Wood GM screen with hinges? Character boards made of laminated wood. And of course some kind of soft insert form to put the miniatures in. No resin 3d dungeon, sorry.
That's about all I can think of. This way it's not imposing a lot of homebrew stuff, and its giving the player the "best" of both worlds.
The only other issue would be if both sets of rules are included, the Spell and Equipment card text doesn't change. So you'd really need an alternate set of cards for that. So I guess there is still a need for localization there, but the dual rule book can still be included to show you what's what.
So re-release the Japanese version too (and finally give them the expansions... now THAT would be a lot of work).

My dream for a remake like this would never happen until such time (if any) that Hasbro and Gamesworkshop were back working together again like the old days. Then they could include Warhammer-esque world maps, Chaos Warriors and Fimirs, classic artwork, etc.