It wouldn't make sense to have Richter. It takes place after the events of SotN, but not right after. This game takes place after the Belmonts have disappeared until 1999. No returning characters should be in other than Dracula and Death, especially not Richter and Alucard.
it would make more sense than for example portrait which brought back the zombies of richter and maria back after 100 years.
sure, one could explain "but, it wasn't really richter!" and yes, it wasn't him during the whip battle. but that was in another dimension, which the memory of the whip more than likely couldn't leave, not even being real.
and then, where did maria come from? she never used the whip, so it couldn't remember her. the extra modes make no sense story wise, they're just there.
unless ooe happens during bram stoker's, richter and maria should still be alive somewhere, old or not depending from when does the game happen unless they got killed john style, so their mode could always be a possibility, even if like portrait's "for the lulz" mode.