I've been running an 11-speed road cassette on a 10-speed MTB hub by removing the 11-tooth cog and putting a spacer behind it. I know a lot of people resist this kind of change, but it's been working great for me.

The other issue that was only briefly touched on above is the problem of rim width with road tires. While 700c and 29er wheels have the same bead diameter, there is a limit to how wide a rim can be and still work with skinny tires. This limit is beyond what the typical charts you often see claim it is, but it's still there. I wouldn't try to run a 700x25 tire on a rim with a 21mm internal width.