I think based off of a likely bad Trump approval the reps pick up 2 seats in MO and IN while losing NV/AZ an maybe either TX due to Ted being Ted or UT due to thrid party so a range of +1 R to +1 D seems reasonable. While in the house pants a much easier path for dems which I why I'm very confident in a D flip in 2018
Seems like this. But my projections are more D-friendly that I'm going to say the democrats will hold all seats they currently have (including the top 2 toss-up GOP targets of MO and IN; I'm not ruling out a GOP margin of 5-10 points, despite the odds) while picking up NV; secure a net 10 governorships' increment; and finally, narrowly filp the house.
Folks might laugh at this post though, by December 2018.