This would be an opportunity for the BBC/ITV/Channel 4 service Britbox. They could remake Blakes 7 without having to consider an American audience.The main issue in my opinion is not the replacement actors but the writer and director. A show lives and dies by it's script and direction, and there are precious few of the Calibre of Terry Nation and David Maloney. Just compare the writing on Doctor Who now to it's hey-day In the 70s and early 80s.
It's extremely likely that if the show DID make a comeback (and if Lost in Space can, why can't B7?) that it would be produced by either Netflix or Amazon Prime - and that is predominantly for an American audience, not the B7 fanbase. But when you consider the calibre of some of the shows that have been created (esp on Netflix) a good reimagining is possible. Like I said the premise is still solid and as relevant today as it was back then - in fact perhaps even moreso.