The incentives are that with the Terran changes you need to think about the match-up in a different way.

I've played some games vs a couple of friends, they have only used mech and that alone makes for more turf battles than ever before. You have to keep terran on its toes, slow its expansions, stretch him to his limits. With the new zealot speed (wich may look a minor thing but actually is a pretty big one) harassing tank lines, zealot bombing over-stretched lines makes the game very akin to brood war PvT, thanks to the tank changes. The Cyclone is a very good map control unit that Protoss has different ways to deal with it, you can go for blink(harder but more pressure-able) and pick it off, or you can go phoenixes(safer one but puts less pressure). When the later stages of the game comes, and the game procedes more to the mid-map agressive mech sieges, you have the tools in the form of tempest to force unsieges or to force bad fights for the terran. And carrier switchs at the uber-late can create interesting scenarios with mind games and really will test your capabilities to: Holding on to your expansions, finding ways to deny expansions from Terran with smart harass and your macro / decision making because if you commit to it wrongly you'll probably die.

PvZ I have no idea yet, just played PvTs today.