So I got these in the mail today - and wow - I'm totally shocked, I hadn't looked at any of the online photo galleries close enough, I had just assumed that the outer shell part of the droids' bodies were all the same - nope - BB-9E is completely unique, while 2BB-2 & BB-4 do share the same body shell, but they have unique "domes".
Additionally, BB-8 and BB-4 share the same weighted ball sculpt, where 2BB-2 and BB-9E have a new unique weighted ball sculpt.
So basically, in the BB-Unit Droid Factory line, we now have the following unique parts:
2 Different Weighted Interior "cores"
3 Different Top & Bottom Exterior "shells"
4 Different BB Unit "domes"
So A LOT more variation than I originally thought there would be.