Shame it didn't end up as a Colin story, your Excelis Rising was superb, easily the best of that trilogy/quartet.
I'm *told* that Tony Head agrees with you. But the other writers were probably told the same!
Colin's very good to write for - I didn't like his Doctor on TV, but he's easily my favourite audio Doctor. If Unregenerate had had him, it wouldn't have had the "insane Doctor" bit...
Re BF pitching, I believe these days the way it works for the main range is that, as each Doctor gets three stories in a row in miniseasons, the call goes out to writers "do you want to pitch for our Jan-Mar Seventh Doctor/Ace/Hex series?" rather than inviting pitches for random Doctors. No idea how the Companion Chronicles work though.
I dunno how either of them work now - the twice I've asked since Nick Briggs took over I've just been told "we're commissioned up for the foreseeable future" with an unsaid "so don't fucking bother, OK?"
I did do a Stargate Atlantis that came out last year, but I think really they're ever more in-house, with a little repertory company of writers who've settled in as a staff, rather than a wide range of freelancers. That's how it looks from out here, anyway.