Incursors, Infiltrators, Aggressors... minimal squads, of course. But then again I don't really play 40k (yet), but I think I can see some potential for it.
It can't transport Aggressors (who, I agree, were it possible = no brainer). Infiltrators and Incursors have zero use for a transport and are actually worse with one.
The only useful options are Intercessors, Reivers, and Hellblasters. Hellblasters I'd rather have on the board, blasting away. Reivers I can actually see as being useful, but Reivers are pretty awful so I can't see taking them.
So, Intercessors. What exactly are you getting with a transport option, though? They have enough range that they don't really need
to move much. They don't especially love assault. Shelter from Turn 1 fire might be nice, but it's a steep price to pay for only that, and after that first turn...then what?
I just don't see its use, I'm afraid. Transports in general this edition are just so, so lackluster. In almost every instance I'd rather have more guys shooting.