Thank you for asking, but I probably shouldn't get into that :) I'm inherently conflicted / biased due to designing a solid chunk of Tumblr's backend, and also previously worked for another Automattic competitor (Six Apart, the defunct company behind Movable Type).

Edit to avoid anyone misconstruing, I'm not trying to imply one thing or another, just that I can't approach this impartially. And in any case, I wish everyone well on both sides of this acquisition. I'm just genuinely curious how they plan to proceed from a technical standpoint, as it's a really interesting challenge.