Public Service Announcement:
Illustrator and InDesign have a 27-color limit when doing seps for spot colors.
If you have that many, it’s already too many.
Now back to our regularly schedule program.
I’ve never had occasion to use more than 27 spot colors on a single job, but it’s good to know for when that job arrives. 
In a pinch, if someone really needed, say, 31 colors, maybe the CMYK channels could be co-opted and forced into labor for spot color purposes.
I know a lot of Nail Polish marketing material can go up that high to get all of their colors to show correctly.
Most I’ve had was a 20 color job (double pass 10 station press), but that was only to show off a bunch of printing technologies on one piece.