The only component I want to see in a demo of any UX framework - be it desktop or web - is the almighty tree table. I‘d like to see sorting, filtering, column resizing and -reordering, including save / restore of the above. Row (multi-)selection, striping, hover. Inline editing. Show me all other components inside a row.
Tables can get quite complex as features get sprinkled on. I doubt any out-of-the-box solution will nail it for all use cases. I'm not opposed to including one in Shoelace at some point, but I'd want it to have an API that's capable of handling the majority of [reasonable] use cases in an elegant way.
It's definitely high up on the list of components that are challenging to get right!
