Yes, I think you're right about Andrew, and I don't know if he'd want to do it, whereas Amanda possibly might. I also see Andrew more as the Master but I don't know if that's because I'm thinking of him as Moriarty! Peter Capaldi was very well known before he was cast, but then he was major Doctor Who fan, whereas Andrew's the wrong generation.
Michaela Cole did I May Destroy You which is maybe one of the best and most original bits of TV I've seen in ages (but divisive! Not everybody I know liked it!). She's quite a powerful presence and I can see her as a highly intelligent, funny, slightly unsettling Doctor!
I think Chris Chibnall is leaving as well, so we really don't know what sort of Doctor we're going to get and what direction they'll go in.
But anyway, you've now got me thinking of all of the cast being in Doctor Who, whether as the Doctor or other parts! Mark is obvious, as a fan and writer, but has already been in it (not that it stopped Peter Capaldi!). I could see him as the Master. Una maybe as a companion? Or Yasmin? Lindsay Duncan as the Doctor? Maybe Bertie Carvell from The Blind Banker? I do like the idea of Amanda, though.