The fact is Moffat probably wouldn't have gone for an older, well-known actor. Especially not Paterson Joseph or Derek Jacobi who'd already been in Dr Who... It may've been rumoured that certain people would be selected, but simply put at the time the rumours were everywhere. I mean I remember a rumour spreading that Richard Hammond was going to get the job.
I can see Benedict Cumberbatch being the next Doctor, he did consider it, and if Moffat doesn't have OTL's best consideration for the role Cumberbatch may accept. If Cumberbatch did accept, and I expect if he was pushed enough he would seeing as he's an avid Dr Who fan, that could mean he'd be in both Sherlock and Dr Who, as IIRC he'd already been cast as Sherlock Holmes.
If this is the case his fame will explode even further, and the scheduling probably wouldn't clash seeing as Sherlock had so few episodes.