I bought the 50th anniversary edition of Doctor Who magazine, just to keep as a souvenir, and what do I find it's giving away for free? Big Finish audios! Nine of them, which is awesome.
One of them is Part 1 of Dark Eyes
with Paul McGann, which I've heard good things about.
Downloaded them and will listen soon.
Egyptian mythology gives me the image of Pyramids of Mars and Sutekh (The only Tom Baker story I've seen actually). I'd still be down for something like that though. A powerful God-like creature which requires the Doctors to team up. Perhaps something like the Beast from The Impossible Planet/The Satan Pit.
Then there's always the possibility for a new incarnation of the Master.