I've considered this too, do you think it's possible they might find shortcomings in AP2 hardware and adjust before the Model 3 comes out?
Lots of things are possible. However, they've committed to always having new technology in the X/S first, and they won't really have much fleet experience before they have to lock the initial production run of 3 hardware - if they haven't already had to do that.
My bet is the 3 will have the same AP hardware the S/X have today for at least the first several months of production. I think the next generation of hardware is at least a year out, and quite possibly 2 or 3.
What I'm really not sure about is how the eAP/FSDC rollout is going to go, and whether they'll be able to do "it drives itself, but you have to pay attention and be ready to intercede and legally responsible" in a year or so with AP2 hardware while they try to convince regulators.
AP is already a figurative (and potentially literal) lifesaver on long road trips, but the idea of being able to relax and read or try to sleep while the car does everything is tempting (I'm not foolish enough to try that with an AP1 car even on empty freeways.)