Not sure that counts as a 'massacre'; more a reversion to the mean. Most of those races that are going to flip were competitive anyways. I see no pathway for a 60-seat D majority, and that's all that really matters once you get to 50. As you noted the House is locked up tight until 2020 given the plethora of safe seats. So maybe - maybe we'll see a few more Senate seats shift, which could mean the difference between a small R majority and small D majority. But otherwise I think the turnout etc effects are going to be subdued just because there's not that much that can shift.

I haven't looked in any level of detail on the state level, though - it's possible that some state legislatures may become competitive based on turnout and halo phenomena. Also haven't looked at governorships, where I wouldn't be surprised if Dems picked up a few.

On the turnout angle, though, I think it's not always clear what will happen. There are a lot of people I've talked to who believe in 'anyone but Hillary' - and even if they loathe Trump, will actually vote for him to keep someone they see as duplicitous and untrustworthy out of office. Furthermore, I don't know how good turnout will be in the progressive wing of the Dem party - the rift there is real and even if most of Sanders' camp won't consider voting for Trump, they might just stay home. I still think your broad analysis is correct, but the magnitude of the effect might not be as big as you anticipate.

I'm interested to see who Clinton and Trump pick as running mates. Trump I have no way of predicting, but I wouldn't be surprised in Clinton picked someone like Warren - a woman who comes from the progressive wing of the party and has some national name recognition. Alternatively, a mainstream Dem from an important state (somewhere in the Midwest?). I'm sure Trump will tack towards his version of 'presidential' and try to get a reasonable-sounding VP choice, but I really haven't a clue who that would be.