just my view point, i believe the surface pro 3 case was design with broadwell chip(5th gen) in mind, but delay by intel, and not wanting to missed the back to school season, ms plug in the haswell(4th gen) instead.
that is why all this heat issues. but actually the i3 y series, at 11.5W seems to match the case better. (which the 5th gen i5/i7 chip might be at the same level)
so, best future proofing is buying the specs of what you need now, save the money, when the new pro 4 comes, n ur future needs comes, the money saved can be use to buy the next one instead.
selling features of pro 3 is screen n kickstand, not the processor.
just my 2 little cents... which i might be wrong and you are right. Be happy...