Shifters were Eberron specific and made the PHB2. I wouldn't be surprised to see a Dark Sun race in PHB3.
Shifters? Nah. Those things have been around forever in one form or another. In any case its certainly a race that fits in well in a standard campaign setting, which is I think why it was introduced as a core race/monster. Given that true lycanthropes are a bit out there as official PC races the shifter makes perfect sense in core.
Very true, and an Int one would be good also. Warlocks have few multi-classing opportunities and Wizards have Swordmages only
Cmpared to strength-based multis, most other multis are left behind.
Uh, wizards can MC to a lot more than just swordmage. In fact its really better from what I can see to MC the other way from swordmage to wizard. Invokers are practically a perfect MC match with wizards, they share prime reqs AND their implement, how much better can it get? Its not at all hard to make a wand wizard that MC into rogue either. Orb wizards can do reasonably well as clerics too.
Warlocks CAN MC fine. Paladin is an excellent choice with full overlap of CHA between star/fey and CHA paladin. You can go either CHA/WIS, or CHA/INT depending on what you want to do. CHA/CON is possible as well but splits your prime stat, though it does give you access to more warlock stuff. A CHA/DEX warlock/rogue is also an interesting choice.
An OBVIOUS choice would also be a Summoner wizard/conlock, though I'm not really sure what would be gained by it there's probably some sort of fun build hiding in there.
I really haven't looked into what would be possible with the primal classes. Several of them depend a good bit on CON so there are possible synergies with conlock or summoner wizards potentially. Shaman is very definitely known to go well with wizard, both being INT based primaries.
So yeah, there are really no other CON primary classes except conlock, which does limit them a good bit but with the right choice of race you can do something. Dwarves can definitely easily pull off a warlock/cleric or warlock fighter.