Schumer thinks dems can get the senate in 2018

[Virginiá]

Utah, via a Hatch v. McMullin v. Matheson/McAdams slugfest. Texas and Nebraska would vote for a convicted criminal with an R next to their name over a Dem.

Democrats held Nebraska's CI seat for almost all of 1977 - 2013. I think it would be difficult for Democrats to get one of Nebraska's seats, and maybe it would need to follow a similar pattern as before (State Executive office -> Senate), but I don't think it is as impossible as you are implying.

At any rate, like xīngkěruì said, Schumer, as minority leader, is obligated to say things like this.

[Virginiá]

He doesn't have to say anything about the odds of his party winning control. He could say "Sorry, but I'm not the chairman of DSCC any more; my crystal ball is on the fritz, so I can't and won't try to predict; my job now is to govern, not campaign."

Yes, that's true, but he's being optimistic for the team. If the fight is almost impossible, it would be best to try and motivate your party and not try to squash their hopes, even if you do ultimately see little chance in winning a majority. I mean, look at it this way, would it be preferable for a coach to tell his team, "the game is pretty much done, you can't win, but let's get out there and play, I guess?" Probably not.

[Virginiá]

What state legislatures are even possible to flip? The rural/urban divide makes it unlikely to flip almost any state legislatures

Colorado is basically a given. New Hampshire, Maine, Minnesota, Washington (this year's special election might do it for Democrats, though). There are even more targets in terms of single chambers, giving Democrats a chance to break GOP control even if not seizing control themselves outright.

I think a lot of the state-level gains would be in the form of those^ legislatures above and hopefully sweeping gubernatorial races, which would give Democrats unified control over a lot more states. After all, GOP governors in states with Democratic legislatures do bring down the unified control count a fair bit. An incredible year (keyword: incredible) could leave Democrats with upwards of ~16 unified state governments and more split GOP state govts.