It's interesting to see the ideas people have, there are a lot of strong ones with some very weak ones mixed in, which uh, I guess that's D&D in a nutshell! Like, alignment, bless its heart, is no more going to make a comeback than racial level limits. The most successful edition sees truly massive player growth whilst not using alignment in any meaningful way, having it be almost entirely optional? The most successful D&D videogame doesn't even acknowledge alignment exists? Critical Role doesn't mention character alignments in S3 and leaves them blank on the character sheets? Yeah that's a sacred cow so dead even True Resurrection isn't going to help!
Personally I'd want to see:
1) CON either justifies its existence as an actual stat, or else stops being a stat or is removed completely. Right now it's just a weird place you put your second or third highest stat to make you have a lot more HP, and it's actually quite limiting to how people, because unless you do that, you do actually have quite noticeably less HP and consequentially, survivability. I see way
2) HP start higher, increase steadily until about L5 to L9 (wherever works best), then slow to a crawl after that. Monster HP is scaled accordingly too. This means we can keep damage much more under control, keep abilities, spells and monsters more relevant for a longer time.
3) Spells approached more like other modern D&D-type games, where all spells can potentially fail, absolutely including utility spells cast outside combat. Maybe let slow-ass ritual casts have a very high chance of success, but generally spells should be at least as risky as skill checks, ability checks, and so on.
4) Serious rationalization of spells, no spells retained solely because they were popular in a previous edition. Look at the mechanics now, see if they're worth casting, if not, change them or remove them.
5) No use of spells as faux-abilities. People can handle it. If your proposed ability is identical to spell, probably rethink one or the other. A certain proportion of spells just shouldn't exist anymore (3 & 4 will naturally lead this way anyway).
6) Completely change approach to backgrounds.
7) If the game has three pillars, support all three pillars. Currently 5E flatly does not. It supports combat, and vaguely acknowledges the other two exist, but barely lifts a finger towards them. Rethink everything in the game around this. People who like this specific kind of game will have more fun if combat, exploration and social really are things with some actual rules. All classes should have abilities for all three. All classes, no exceptions, no reliable on subclasses, etc.
8) Hard look at classes and what they represent. Classic D&D Monk should be a subclass and/or specific level-up choices made of a broader unarmed combatant class, for example.
9) Use the advantages you have as the biggest game and the biggest budget. Don't rush the game out. Playtest to hell and back. Balance balance balance balance, and don't listen to provably wrong people who say you can't balance - 5E being more balanced than any previous edition shows how false that is. Make sure the art is devastatingly good.
10) Hire art directors and artists who understand the difference between cute/charming and "twee". Remember this an RPG about adventurers, art should reflect that, this isn't, for better or worse, a more sim-ish game about fantasy societies and so on.
11) Launch with actual free digital support that is high-quality. Don't launch if it's not in place. Again utilize the advantage you have as "the biggest" here. Stuff other companies can't afford at all is a pittance to you.
12) As part of balancing, ensure all the stats are actually used and useful. You've got three pillars of the game that need mechanics, so this should be pretty doable.
13) Redo surprise and stealth so they make intuitive sense.
14) Accept that this will be a non-backwards-compatible edition.
15) Focus on making the game actually fun to play. This might seem trivial, but seriously, this means working out what people actually enjoy about it, what is satisfying, what is rewarding, what is compelling - again as the largest-by-far company this is a place where WotC could use their advantage.
I could go on. But WotC are really failing to leverage what they've got over other companies, frankly. 2024 moved a bit in that direction, but not very much.