PvT - Big Economy Zealot-Archon Build
Back in WoL, I used to do early DT harass into 10-gate zealot/archon as my main build. When HotS introduced the widow mine and fast medivacs, for a while I thought my build was dead. But I think I've finally solved how to do it.
Gate-core expand (specific timings 9 pylon, 13 gate, 14 assimilator, 16 pylon, 18 core, 21 stalker, 23 assimilator, 24 pylon, 24 MsC, 26 Nexus, 27 Warpgate)
Sentry-Pylon-Double Forge-Twilight Council-Stalker
1/1 upgrades
2 Photon Cannons-Dark Shrine-Nexus-Stalker
4 Gateways-4 Gas-Robo
Blink-2/2 upgrades-More Gateways
Use the probe that builds the Nexus to check for any proxy buildings, then send it to a watchtower to watch for early pressure. Scout for their base if it's a 4-player map. Send it home when the stalker is out on the map.
The first stalker should head for the opponent's base as soon as the MsC pops out to check for their expansion. The MsC can also do a mini-scout along the back of the opponent's main, but make sure to send the MsC core home by 6:30 in case you need to photon overcharge for defense. The 1st stalker can stay out on the map to watch for pressure.
Your 3rd stalker and 2 cannons should finish around 7:15 which is the time when the standard widow mine drops occur. You'll have 2 stalkers (a 3rd watching for front pushes), a sentry, MsC, and the 2 cannons, enough to defend with, and he won't have any more than 1 medivac.
This drop will either delay or severely weaken any follow-up timings, so if you defend it, you'll likely be safe until at least 10:00. The 3rd nexus can be delayed by up to a minute if it has to be.
If you see any big ground pushes between 7:00 and 9:00, then the opponent is most likely all-in. Cancel the 3rd and get lots of gateways, a 3rd gas, plus a robo. You;ll have two photon overcharges available by 9:00, so the natural can be done twice starting at 8:00. Try and sneak a probe out for a proxy pylon for a potential DT counter during their push. They most likely won't have turrets at home to defend it.
If they haven't attacked yet, it's a good idea to use a hallucinated phoenix or oracle from your sentry around 8:00 to see what they're up to.
9:00 are the earliest medivac timings if they don't put on any early pressure. For this you'll have 5 gates with more on the way, 1/1, and 2 photon overcharges, plus the ability to do DT counters.
You'll want to try and go up to 8-12 gates before going for your splash damage units (colossus, high templar). This is because you'll need to rely on a bigger economy and therefore army size to win your early engagements. Zealot-Archon is really good against MMM without ghosts, and blink stalkers aren't bad either for sniping stray medivacs.
I think I'll leave SCFusion running a little while longer to see if it comes up with anything better.
In PvT, I think the long-run direction is either going to be towards fast thirds or phoenix builds. The fast thirds will rely on bigger economy to deal with medivac harass in the mid-game. The phoenix will shut it down entirely, and force direct engagements where forcefields can be used. I think it was MC who was quoted as saying that the reason he was doing so well in PvT is because he's playing HotS while all the other protosses are still playing WoL. A lot of tosses are still doing 2-base tech plays where they go for fast double upgrades and colossus or fast storm before expanding. The new medivacs are forcing those players to waste a lot more army than they're used to for defense, take super late thirds, and then play catch up the rest of the game. That's not going to work long term.