I am not sure that AB * 2, AM spam will be bad after 2.3 as the mana regen increase will keep you in mana. With the MSD not proccing as often, but more 'regular', you can always hit AM when it procs as opposed to now, when sometimes it procs back to back to back (your threat jumps up a ton, as I was running with BoW instead of BoS due to the 40% threat reduction from arcane).
Did this last night in kara with my mage (hesitantly), but found out that I did fine with my 49/12/0 spec. I topped the meters above 2 rogues and 2 locks (which was way fun). Even during nightbane, which I was probably the most afraid of due to the length of it, I didn't run out of mana. Had a shammy with mana tide and 2 evocations to use + pots and gems. With the increase in arcane meditation as well as the improvment to evocation, arcane is still viable in kara. ;-) I am not sure if I would do as much damage as fire or not (10/48/3) as I would lose some spell damage and arcane gives you a bunch of +hit too. I had around 1140 spell damage and it was *hot*.
I'm going to keep my spec until a run or two after the patch, then respec to 10/48/3 and see how it goes.