For starters, real text handling. Just doing a full text widget with all the trimmings is quite complex problem. Druid has made good progress on this front but

For starters, real text handling. Just doing a full text widget with all the trimmings is quite complex problem. Druid has made good progress on this front but is nowhere near where it should be. I also put IME in this category. As mentioned elsewhere, accessibility. Aside from web technology, Qt is one of the very few cross-platform toolkits that gets this right. I'm happy to see that some other projects, egui in particular, are starting to pay attention. One of the things that Druid doesn't do well right now is integration with 3D and video content. That will depend on the application (it's not needed for font editing), but is definitely needed for a toolkit to be considered general purpose. The implications go deep, mostly because you have to hook pretty deep into the system compositor to do this well. I may do a blog post on these infrastructure topics, depending on interest.