Republicans are very overextended in state legislatures, so there could be huge gains among Democrats if it's a wave year in 2018. The most plausible chamber pickups for Dems are the Colorado Senate, Maine Senate, Minnesota House, both New Hampshire chambers, and the Washington Senate. The second tier targets for Democrats are both Arizona chambers, Florida House, and the New York Senate (if the IDC is primaried), and the Virginia House.
The "wild cards" are both chambers of the North Carolina and Wisconsin and the Texas House. The legislative districts were ruled unconstitutional, so we don't know how the new maps will affect the outcomes.
I think the NH Senate might be tough given the gerrymandered districts in the state, but it's not impossible. The massive state house, on the other hand, is prone to wild swings and could easily flip if Trump's current popularity levels last into late 2018.
