I use this too in some of my shaders. And since i put them from xna to mg it builds with errors. I m curious to know why this would not be a valid call to a pixelshader method.
When I scratch my head during a whole afternoon to finally discover my problem was coming from a monogame limitation I keep wondering.
I would be able to circumvent this limitation about uniforms by passing parameters as it is done with setvalue but I dont know if it would be a long term solution.
Compute shaders too is a really big limitation… For ex to make advanced god rays like fallout4 without a bit hit on perfs (im thinking about conetracing and tesselation) distance fields etc.
Compute shaders are not the priority but when i will need them ill switch to sharpdx or i ll contribute to monogame if i have time