Blake's 7 would have to be a re-imagining ala Battlestar, instead of a continuation.
The actors made that show it's original iteration. And while I can see new actors doing different versions of Blake, Avon, and Vila, I'd never buy new actors pretending that they were the exact same characters picking up where things left off.
Plus, new viewers would be so confused. There's just so much history, betrayals, and such.
A new version could be great, presuming the writers are willing to kill of characters, and not in the same manner and order as in the original show. Things should eventually go spinning off in a different direction that's no less brutal...