I wouldn't rule out the return of an old school companion retn totally, but it may be done with a different spin as in School reunion. I re-worked version of , say Big Finiish's THE GATHERING could work, showing the negative impact of travelling with the Doctor following their adventures, or visiting a companion who has turned out to be a meglomaniac or something or whose actions have had an impact in the future/current adventure.
I remember a DWM "brief Enounter" story about some companions getting together following an advert asking if anyone knew what TARDIS meant to get in touch. I think that would make an ideal "Dr Lite" episode if that concept was ever revisited, but I'd assume that Smith may be contracted to 14 eps a year?
Plus further to a post above, why would being in Being Human prevent Tovey doing Torchwood? BH is only 8 eps long and already filmed....