If you were going to pick one "type" of thing to be expanded significantly by a new WotC products, what would you most like to see addressed? In other words, what needs the most additional options added to the game right now?
First of all, let's point out that your poll is more focused on the
delivery methods of what you call "options". It would be perhaps more important to poll about the
actual benefits, such as "does the game need more options for combat abilities? downtime activities? social encounter abilities? adventure design elements?". Monsters actually belong to the latter, so I think they are somewhat off compared to the rest which is mainly players-oriented. But nevertheless, let's play along with your poll
Personally I vote for more
feats.
The main reason for this is that feats are very much an individual character's customization option, meaning that the character doesn't have to belong a specific group in order to take a feat (although those few feats with requirements kind of implies that indirectly). So for example when your Wizard character chooses its archetype, you know you'll get the same abilities as everyone else of that subclass at those specificl levels, while when you choose a feat it feels more
personal. Of course there can be others taking the same feat, but the
feel is that the choice is at a lower level of details. Naturally, people who detest a game with too low level of details also hate feats, but unlike almost anything else in the game, you never have to take feats if you don't want to.
More generally, I also think that actual feats are still fairly scarce. In theory, there are ~80 feats in the PHB, but still you end up feeling like you have maybe half a dozen of them who make sense for your PC, and so if you like complexity and want to always take a feat instead of an ASI, the feeling you get is that you almost have no room for variations, unless you decidedly deviate from your character concept. The addition of racial feats in XGE did not really change much, since each character get maximum 2 possible racial feat to choose from, and usually 1.
The design room offered by feats in theory is immense... and being basically a one-level-worth abilitities, they shouldn't even be that hard to design. Unlike spells, they don't have to be restricted to a specific class or two. Unlike subclasses, you don't have to push hard to find a strong narrative into them, although you can do so if you want. And unlike both race and (sub)class, they are something you don't have to plan since the start and then be stuck with them, but you can choose along the way, so there is less pressure about the choice, and more opportunities to use them to tie the character development to the story.
Edit: magic items would be my 2nd choice, but I am afraid they might too easily end up with items that simply replicate spells effects, so that in practice they give non-spellcasters the same. Or worse, magic items that would totally steal a class' precious unique feature, such as what metamagic is for the Sorcerer (although that could happen with feats too).
