SPOILER! (select to read)One thing I do remember about the early/mid 90's was a strange trend for American shows to do better over here than back home (in terms of percentage of the population watching and what Channel 4 or whatever would consider a success compared to NBC). The aforementioned Dark Skies and American Gothic,Babylon 5 at one point had 4's highest AA index result (for the end of season 4, they then promptly dumped the next season in a rubbish mid mourning slot) and most obviously Due South which the beeb would up financing (and as soon as they put money into it they dumped it in a stupid mid mourning timeslot, I spot a pattern). Plus things like Superman pretty much carried on as strongly over here after it had started to die in the States. Even the X-Files came close to being cancelled in America during the second season whilst the first was making great guns on the beeb.Whilst it's not impossible he's playing a regenerated Master the fact the only photo we have of his is standing next to John Simm (in different costumes suggesting they weren't filming a change over) makes it likely they're different characters. There is a chance he's a fraud with a Time Lord costume, but I'd be surprised if they did that so soon after The Next Doctor.
In terms of easiest to bring back Rassilon (dead anyway but some sort of computer ghost, would actually give them a way to feature a Time Lord without bringing more back) or Omega (off in his little Universe) would probably be the best bet.
Blimey, remember the days you were entirely dependant on wacky TV stations to actually see the latest episodes of American shows? It was like the dark ages.