You could vary the heights, but it would have an effect on "clutch power" (how well the bricks stick together), and Lego is very big on making sure that's up to standard. Its often what separates Lego bricks from clones. Also you'd struggle to make a kind of braille pattern on some pieces, like 1x1 bricks.

You could try to make the tops of the bumps textured, but that's where Lego puts their trademark, and I don't think they'd compromise on that, since its another protection against fake bricks that claim they're Lego but are worse. I also don't know how well you could feel textural differences in an area that small

I think that idea is worth testing. Putting a symbol on top of each stud. There could be a tactile symbol per color.

I imagine an aftermarket machine to heat-stamp this on. It would have to be very precise. Pressure would displace plastic and easily change the clutch power.