Im hoping they'll do it so that its always time vs money.
So nothing goes in that couldn't be gotten eventually anyway in game and of course, no rare or majorly game changing equipment purchasable.
Of course chances are they will want to put some otherwise unobtainable items in the store (the game companies always do as it tends towards forcing people to pay) in which case getting stuff to spend in the store with your subscription is a reasonable solution.
That said, this may break the game for me if they go overboard on the shop, I've never liked micro-transactions with my games and I never will, but I can accept them to a point.
The minute special weapons and armours start popping up and stuff that is "must have" but purchase only, that's the point I (and I dare say a fair few others) will probably leave.
And this would be a shame, AO has been a big part of my life and I'd hate to see it destroyed by some money making scheme that seems to be along the lines of "they did it so were doing it too!"