If they created a Doctor Who ride they wouldn't base it around one monster or creature, it would most likely be an 'adventures of' ride.
The idea of a ride that concentrates on The Paternoster Gang (Vastra, Jenny and Strax) would be interesting, and they do have a certain appeal, although I'm not sure if that appeal is strong enough for a dedicated ride surrounding them to be made. If there was a spin-off show surrounding them already on TV I would probably say that's a great idea for a ride. Unless BBC Worldwide have some market research that supports their popularity for Merlin to go ahead with that kind of theme.
I quite like all this London Victorian speculation though, with or without an IP it would be a pretty interesting theme.