I want to see how will Moffat's era end, if Capaldi does decide to stay. With RTD, he basically used Ten as his avatar, so when he said "I don't want to go," I actually think RTD didn't want to go, but decided he had to anyways. So Ten's "death" was literally RTD's exit, thus why Eleven's first words were literally Moffat's first, as well. So barring the exit of a Doctor, I wonder how will Moffat signal his exit. If he did leave with River, it'd have been perfect, cause she, more than anything else on DW, represented his era - the good, and the bad. So what now?
I realize I strayed away from the companion talk, but to me, until we get an announcement, its just speculation. The only thing I'd say is, that I agree with Wormhole wholeheartedly - the Doctor needs a companion, and it needs to be of a different ethnicity.