The 9001 will most likely work with the 1x. The difference is in the spacing for the 27-31 and 35-40 sprockets. The chainline and spacing has to be adjusted so that the system can crosschain with the triple front chainrings. Not sure how it affects the 1x system but I'm willing to bet it won't make much of a difference unless you're on Di2, as you can adjust your limit screws on the mechanical system to get the derailleur alignment sorted.

And yeah of course I'm on di2...guess I'll pay up for the people cassette or go with XT

I'd agree and go with it would probably work. But hard to be wrong on such an expensive cassette.
I found the specs for the 3x11 unit and it says the 11-24 rings interchange with the 1x and 2x - but the 27-40 don't.

I can only imagine it is chainline issues, but I think the spacing would be the same distance for each one gear shift. Maybe just different ramping?