I agree on the premium necks as there's definitely a market there for people who are happy to do a scratch-build body but are happy with a pre-made neck (like me!).
For me premium kits aren't as much of a draw, but I fully get that they are for many. As elcoyloco says, there's a sweet spot in what's currently offered.
The only other thing would be expanding the range of hardware to provide an alternative to the likes of Realparts or Stewmac. Then again, that's a lot of inventory to carry.
As far as the premium kits go, I'm guessing you'd only offer them in a limited range to assess interest?