There has been a slow shift in metagame for the TvZ match up. Perhaps, a more accurate way to express it is that Terran is trying to break the current metagame.
Let’s trace back to the last major patch in November 2013.
Widow Mine got nerfed. The 4M style has suffered due to the less ineffective area effect cover against the swarm of Zerg units. When Terran realise that Tanks still don’t cut it, the metagame maintained the same for a period of time right after the patch. Thus, Terran got nerfed in TvZ. The main reason for Terran to stick to the 4M style is simply because it was (and probably still is) the best play style in TvZ. You may have watched Day9’s analysis of TaeJa’s TvZ style after the patch, whereby TaeJa made tactical changes to adapt accordingly. Nevertheless, the core of the style is intact.
Credits to TaeJa, he might be the only Terran who still enjoys that degree of success in the match up after the patch. Even the TvZ god, INnoVation, was suffering. INnoVation decided to discard Widow Mine altogether and tech straight to Thor. But it didn’t work out as he was crushed by Life in Dailymotion cup.
Since then, Widow Mine has been a “hot and cold” unit in the match up. Some players (e.g., TaeJa) still use it like before, while others are trying to play bio without Widow Mines. This is evident in Bomber’s games. He was using the usual 4M unit composition against Scarlett in IEM Singapore. Bomber then mainly used either pure bio or bio Tank in the following week against Soulkey in the Hot6ix cup. That was the state of the match up at the end of 2013: Terran had yet to found a main stream style against Zerg since the patch. Thanks to the concern surrounding the TvP match up, the TvZ match up had not received much attention.
Fast forward to the recent Proleague games. Flash was producing Hellbats instead of Widow Mines against Rogue. It might be due to the Roach heavy composition that Rogue was using. However, as the game stabilizes to later stage, Flash still did not opt to produce Widow Mine.
What about mech? More and more Terran are using mech in TvZ after the patch. This trend was obvious in IEM Singapore. Mvp vs. Curious and Happy vs. DRG were just some of the examples in the tournament. But the mixed results of mech had yet to convince me that mech is the answer to the match up after the 4M nerf. Most recently, Flash used an interesting opening against Solar in Proleague.
10 – Supply Depot
14 – Command Centre
15 – Refinery
16 – Barracks
The interesting part of the build the order of barracks and refinery after a 14Cc opening. In general, you open with
10 – Supply Depot
14 – Command Centre
16 – Barracks
17 – Refinery
Flash went for a refinery before barracks. This allows him to build the factory and reactor at around the same time. In short, you skip Marines for earlier reactor Hellions. Although Flash made a pair of Marines before switching the factory on the reactor due to the Zergling at the ramp, the idea is obvious. He then followed up with cloaked Banshee to transit into a standard mech. This build is likely to get punished hard on a two-players map.
The merit of this build on a big map is that you can apply Hellions and Banshee pressure earlier. Apart from the face value, the earlier pressure allows you to play slightly more greedy behind it than the “standard” mech builds. Flash went for a third command centre and followed with two armory for upgrades. Usually, you will add two factories and an armory after the third command centre.
All in all, mech is still far from solid in the match up. Despite the frustration of using 4M, I can see players swapping between the two styles until an actual metagame shifting innovation is done.
TerranCraft 
Your metagame analysis is interesting and accurate as always. Mech I think is completely underestimated. A big weakness of mech was the roach-hydra timing once scouted. The fact that banshees now share upgrades with mech gives a very nice screening force against roach/hydra. MVP did a 2-2 mech timing against curious multiple times and curious was just helpless. The fact that banshees are also the counter to swarm hosts also makes mech very powerful currently. I expect to see much more mech play in TvZ once people realize how good it is.
Another powerful timing Innovation has used is to get stim before +1/+1 which he used to beat Life on Yeonsu at dreamhack. It’s an old timing that hits at 10 minutes with upgraded marines and 2 medavacs, but still quite powerful. Zergs are still the reactive race after all and can be punished with a variety of timings if they don’t expect it.
And lastly I like to point out that tanks are still buffed and that means there are holes that can be filled by them. Bomber 4-0’ed Jaedong just doing a variant of triple orbital 4m that gets 3 tanks first slightly delaying upgrades. Granted this was before the mine buff, but with the tank buff, I think you might see this build still be quite viable especially if clever players find ways to exploit tank positioning in the way clever players use to exploit bunker positioning.
What’s clear is triple orbital into 4m is no longer the powerhouse it was that always put zerg on the backfoot as long as you had decent macro. Diversity in the matchup is quite good for the game as are balance changes that aren’t completely one-sided nerfs.
Welcome back from the winter break. There are very few strategy sources for us terrans out there. Yours is probably the best.
For the Mvp games, I was more impressed by his 2 base timing with Thor and Hellbat against Curious. It was anti-meta. Nowadays, when Terran go mech, Zerg will go straight to hive with some Mutalisks on the field. The timing totally kills it.
Pretty interesting that you mentioned Banshee as a counter against Swamp Host. I assume you will combine it with Raven for detection. Happy tried to do it, but it didn’t seem to work out. I must say I’m skeptical about this.