Frankly, I'd be 100% on board if they pretty much undid all of the original metamorphosis. I always liked core sets, though I understand I have a personal bias. Even though I play fairly competitively, many of my friends and loved ones I play with are more casual, and I introduce new people to my -horrific addiction- hobby all the time. Core sets are great for this: they allow for essentially free-printing of all kinds of neat cards/planeswalkers, without worrying too much about making any kind of sweeping narrative. Just cool fantasy stuff from a cool fantasy game. Exciting? Maybe not, but trying to make everything exciting just makes everything boring.

As for 3-block sets, I always felt this was simply a misidentification of the problem. Wizards seemed to blame the missteps of some smaller/third sets on simply being third sets, when it reality it really was the combination of questionable design/development and simply being third sets. Avacyn Restored, Dragon's Maze, Journey into Nyx (with special accompanying act Born of the Gods), hell, even Rise of the Eldrazi if you feel a bit feisty: all of these sets weren't just lukewarm third outings because they were third. They were lukewarm because they either:

A.) Were notably boring and/or underpowered from a design/development perspective (hello Dragon's Maze and Journey)

Or

B.) Were a huge departure from the previous two sets in terms of mechanics and/or tone. (Oh hi there AVR and ROE)

I personally believe that a third set done right, with both the strong narrative and mechanical impact to really bring it's plane's story to a close, could be an incredible success. Also, as a small related side-note (since this post is already waaaaay too long), three-set blocks are hands down the superior vehicle for narrative. The classic Setup-Conflict-Resolution archetype exists for a reason, and trying to set a "newfound focus on sorry" alongside a narrative-killing set crunch was always a baffling move to me.