There are a heap of places where you want a nice select input widget, either a single entry, or an freeform text but with autocomplete, or only accept certain tags.
The widget used by forms lib is really glitchy and has terrible UX. The UI jumps around as you type and the styling and keyboard focus are weird.
I would propose we pull in a decent modern library and then redo the various formslib elements to use it.
Select2 is really good but it is jQuery based. Tom Select looks like the good candidate:
There are lots of places were a good select widget can be used which aren't obvious, for instance the new activity selection modal could just be a styled select widget.