It should be made clear that the new K9 trailer is based on the forthcoming Australian produced series with the new look K-9. It's unconnected with any part of Doctor Who as K-9 is a seperately owened entity.
However, the "classic" K-9 will have much more of an appearance in the Sarah-Jane season, he's out of the black-hole cupboard, and back in the real world, where he and Mr Smith will enjoy a somewhat snarky relationship as to who is more help to Sarah-Jane and the kids.
Oh, and the Cybermen have never been purely mechanical, otherwise they wouldn't be "cyber" anything, they'd be robots.
It wasn't a budget consideration, the original Cybermen were ALWAYS intended to look partly human. Hence the very first design (which the legality page image resembles but is different from) having human hands emerging from the cybernetic arms. They didn't have faceplates either, they had silver cloth stretched across their faces (or what was left of them) so that it was clear that there was still SOMETHING organic capable of movement under there, but it might just be exposed skull for all we could tell.
And the Doctor's appearance in "The Wedding of Sarah Jane Smith" in three weeks time will lead into "The Waters of Mars"