Same has happened around Doncaster also.
However Virgin already had presence and CityFibre have now installed FTTP.
Virgin and CityFibre are rivals, and its unlikley they will want to share infrastructure. Virgin were on about creating a Wholesale network (the same as BT Openreach and CityFibre) so other ISPs could access their network, though not sure if thats still happening (read it on ISP Review a while back).
Its all about competition really, if Virgin can steal customers away from CityFibre (I personally cant see how that will happen given the costs VM charges after initial contracts) they will try and do so.