If Mei's yandere tendencies continue to develop then shifting to Riley will have consequence, most likely for both the MC and Riley. The severity depending on wherever or not the MC willingly shifts to Riley or remains loyal. Yandere's are very possessive by nature so they will often isolate their love interest if they believe there are rivals who threaten the relationship, even going as far to eliminate those rivals. Their reasoning often being "It's to protect us"
If the MC wants to intentionally leave Mei then she may try to eliminate him out of jealously with the reasoning of "If I can't have him no one can." The player will have to be careful not to break her trust and to maneuver into a position where she can't harm him if he's going to survive. Should be interesting.
That said, I would like to see a Susan main route too, so that the player can shift to her on Akame's route.