Just an aside, I'm a mid masters protoss, nowhere near good sadly, but I can at least draw some decent conclusions from what I saw hopefully!
As far as recall, Supernova started CC first into 2 rax 2 gas. This is fairly standard, but instead of spending his gas on tech labs/reactors, Supernova used that massive influx of gas to make a fast factory and starport while pumping marines (hence the early lost stalker for MC), allowing him to control the xel'naga (this won't work on maps where the watchtower isn't shaded and doesn't control the middle as well, just as a point of interest). From there he got banshees with cloak (also again map infrastructure allowed him to sneak the first banshee around into the natural. Maps with different watchtowers may not have allowed him to do this). Combined with the early watchtower control with the marines, this meant that Super avoided a common problem with slow banshees, getting spotted. From there, the banshees in the base forced the two created observers to stay at home (I'll talk about the implications of this in a bit), while Super got a relatively fast third base. From there, MC got a fast third base, which allowed the banshees to be much more successful than they perhaps "should have been" (this is most likely the fault of MC, again explained below). I'll post a link to the replay as soon as I can find it so you can watch the rest of the game, but this is the basis of the strategy.
Just want to go over what MC did, basically standard play. 1 gate expo into 3 gates with a robo. He also got 2 fast stalkers, one of which died early to the marines at the watchtower.
Phew... Sad for MC cus he's my favorite player, but jesus those were some well planned strats from Super... I'm really not even sure how to deal with that! The obs come out too late in 3 gates into robo in order to scout the banshees early enough and then the obs are preoccupied with the banshees, and you can't leave your base to threaten the fast third because of the banshees, and then the drop comes as well as a push to the third.... I'd like to see it attempted on some other maps first though before I make a judgement... Daybreak's access to the mineral lines and Banshee parking spaces and drop angles may have been the key to the success of the build.
... So to sum up what I think, I think if you scout the late 2 rax at the front like that, you can assume 2 rax 2 gas which points to a tech play, most likely the banshees, triggering you to get robo after 1 gate instead of 2 more gates for aggression, pump obs while getting a highish stalker or sentry count (which i prefer to zealots early anyway), and then keeping an obs at your base while forgoing Immortals for more observers. Possibly a blink + collosus allin may be a good follow up to the defense.
Also maps will have to be tested.
I still almost feel that the mere threat of banshees and the forcing of stalkers and the forgoing of immortals and gas expended on obs + stalkers meaning late collosus means that you're behind even if the banshees do little to no damage.... The third base is so uncontested from Terran that it turns into a standard game with noone particularly ahead. But again, i'll have to try to play against it on some more maps... Sadly I don't have a SuperNoVa level friend.
Hope you guys enjoyed this analysis!