-I want more spells, particularly more comprehensive coverage of elemental damage variations. Sure, when I'm the DM I'm happy to just say ray of frost can become spray of lightning or whatever the player wants, but not every DM is so liberal or confident with spellcrafting and being as I'm usually the rules authority for my tables even when I'm a player, asking for my character to get an exception sometimes feels rather manipulative.
-I always want more subclasses. Particularly more that support a comparatively unique playstyle for their class like bladesinger, hexblade, or divine soul sorcerer. These are the sort which both substantially expand options while also being problematic to create on your own (both because they demand more playtesting and because the rest of the table may feel like one player is getting too many special dispensations).
-I'd like more short adventure collections. I find that they seem to provide a comfortable starting place for new DMs and increase the willingness of some people to take on a sessions as DM. Yes, logically there's plenty of stuff made for Adventurers League and whatnot, but more casual players are a lot more likely to buy Yawning Portal, flip through it, and see an adventure they'd like to give a shot at running. The world always needs more DMs.
-I'd like a published final version of the UA alternate class features. I've been playing a Ranger with them, and wow do I like it better than a standard ranger, or even the prior UA ranger. Being unshackled from favored enemy and terrain may undermine the traditional theme of the class a bit, but it also makes them more thematically versatile by the same token. More importantly it makes them equally cool whatever decisions the DM makes about encounters and settings rather than something you have to clear with your DM or take a gamble on. And level 1 is no longer just a crappy fighter with a hunting theme. Also a big fan of giving Sorcerers something, anything, to do with sorcery points at level 2 other than create a single level 1 spell slot.
I would love to get a 5e AD&D: Tweaks and different visions of the existing classes, balanced with 5e, but intended for games with more of a “This one goes to 11” attitude, and more gritty rules modules enabled.
Combine this with an adventure path, and WoTC can demonstrate how different themes can be modeled with 5e.
Agreed. I don't know how much we would necessarily agree with each other on what exactly it should entail but I think having some sort of codified, alternate "advanced" version would allow for the game to continue being inclusive to less experienced players or those who just do better with simplicity, while allowing those of us who would be comfortable with more complexity to have official support for such.