Missing DMU classes right now are 165, 166, 168-171 Turbostars (in planning but no dates given), 175, 185, 220-1 (unavailable for some years now),222 and then as been said a few new classes 195, 230 and maybe the Hydraflex models.
Not sure you can make that claim for Voyagers just because none have been made for a while (which is surprising as they'd probably sell well).
There are some N-gauge ones in Bachmann's list of forthcoming models but not any OO ones (it's a fair few years since the last N gauge ones).