one thing that has never been done is a destroyer droid as far as I know of at least. Theres a ton of prequel stuff they could do.
No one would love that more than I would, but I think that ship has sailed. Disney has no incentive to promote 20-year-old prequel movies and there just isn't as big of fan demand for it as there is for the "classic" stuff from the OT. On the other hand, the new Andor and Obi-Wan shows are both set between the PT and OT, so maybe some PT stuff will show up that can be turned into kits.