Looking at the new Doctor makes me think, wouldn't it be great if he had a male companion? I don't mean a gay relationship - I think they should stay clear of adding a "love interest" altogether - but two lads, two mates off exploring the galaxy. There was some of that with Donna as his companion, and I think, seeing as the new Doctor is quite young looking, having a bloke companion - maybe a recent graduate, that sort of age - would work really well. If you had someone like Donna again, it would look like the Doctor was travelling with his mum. A male companion would give it a new dimension. Then the show could introduce another couple of companions too, make it like it was in the olden days where the Doctor usually had two or three companions on the go at once.
Anyway, just a thought.