Like the title says, update the homebrew system and already existing systems. I mean really the core of DnD is imagination and having somewhere to track it is really all we want. They keep making sourcebooks with 10 new items that no one buys just for us to make hundreds of homebrew every day and deal with broken OFFICIAL features that don't work.

Just off the top of my head I can here's what i can think of:

• Truly custom weapons and armor. Meaning they aren't based on existing ones, damage and AC can be set manually instead of being forced to copy existing items and include tags to make +1, +2, +3 variants without making whole new weapons and armor
• The ability to add options drop down boxes to weapons that augment it's properties like damage type, reach and bonuses on the fly after their in player inventory
• The ability to add option drop down boxes to monsters to augment thier properties like speed, AC, HP, Temp HP, adding actions on the fly after their on player character sheets
• The ability to make general items instead of only magical ones
• Easy tooltip additions
• Feats that level up with class level instead of only character level
• Custom classes
• The ability to replace class features in subclass creation
• Fixing all of Tasha's. There's no sidekick class support and several optional class features have zero functionality

This is just some of the stuff i can think of and run into myself as I'm sure many people reading this do as well.

It is undeniable that the homebrew could be better. However, it's at the point where their options to change anything are slim to none. Getting the homebrew system to be the way we need it to be would be a monumentally herculean task. The system for homebrewing is tied to the system for official stuff. It would involve rewriting huge sections of the coding architecture - they would have to change and update every release since site inception and every existing homebrew would break and stop working. Frankly it would be less effort to scrap the site altogether and restart entirely from scratch than it would be to implement the major changes to get homebrewing where you expect it to be.

When D&D Beyond was made it wasn't designed for homebrewing and the tools for adding content needed to be more streamlined to match the speed of releases and rules validation being required  - when Curse was making the site, WotC told them homebrew was not permitted. Fan demand convinced WotC to change their minds but it was too late to redo the site: it was already up, running and with releases. Curse then made a sort of "lite" version of their own content tools and released those as homebrew. 

So, yeah, it's now too big of an ask. We may see some updates here and there but ultimately homebrew tools on D&D Beyond will never be what we need it to become. There is too much to rewrite, too much that can break, and too little time/money/devs.