They will no doubt keep adding keyrings like this with each expansion. Since we have 2 already, it should be pretty straight forward to add new ones (coding done by JChan and her team is certainly more flexible and forward looking than the coding was in 1999 when the game was built). Plus they get to sell extra slots in the DC store.
I would be an actual feature if they would combine familiars and pet illusions into one keyring and effectively turn all petamorf and familiar clickies into metamorph clickies. In all likelyhood ... the keyring expansion feature will be one of nimbuses, familiars, or pet illusions.