Why then did he do his utmost to be rude, nasty and generally demoralising before he left?
Let's be fair here: Capaldi's Doctor has never been anything BUT rude and nasty to Clara, though occasionally he slips up and shows that he really does care. My read on it is that he believes he cares too much and goes out of his way to put on a show of not caring at all. Normally the balance is there to see, but in this episode he simply takes it too far.
All the same I've been sort of wondering how long she was going to tolerate it. Cranky old men can get away with a lot because they're cranky old men, but eventually the kids start finding reasons not to visit them anymore.
And yes, this Doctor can be quite a prat at times.
...an unsubtle hint that this Doctor isn’t nearly as keen on people as previous incarnations.
Not quite the read I got on that. I think if he'd believed for one second they might actually start shooting people he'd have been standing in front, not behind. I find it far more likely that he'd already noted the lack of guns and was going out of his way to make them feel foolish.
Next week it’s the Orient Express in space, and Clara does not feature in the trailer … will she return?
Doubtful. At least a permanent return is doubtful. I seem to recall seeing headlines before this season (or series, depending on which side of the pond you're on) started airing that Jenna Coleman hadn't signed on for another. That pretty well means that at some point Clara's leaving.
Maybe a companion-free Doctor would be good for a while - fewer episodes set on Earth for a start
Companion-free? Nah. We're way overdue for an alien and/or robotic companion. Unless you count the couple episodes with K-9 there hasn't been one in the revival.