If I was in your situation I'd predict hitting 70 around 2-3 months before Wrath. Now in that situation, unless you are pretty dedicated, you're not gonna get much chance at running Kara+, so what to do?

I'd do the same as I am planning on my (currently shelved) shammy/pally team. Gather up 75,000 honour, 5,000 arena points, and as many PvP badges as I could get my hands on, then wait patiently. Starting so late in the game you'll never be able to catch up to the well geared guys, but you can put lots of "points in the bank" for a great head start in Wrath. When you hit 80, you can trundle off and get a couple of bits of the new Gladiator Equivalent gear and some of the blue PvP bits with all those hard earned points, and a nice head start.

The above is thoroughly possible even loosing 10 arena games a week with the blue rep based pvp gear.

I wouldn't worry about grinding to get exhaulted in all factions, just do all the quests and a few instances and that'll get you Kara entry level gear anyway.

This I think is the most "efficient" use of your time given the situation.