Oh, of course, I know what remixes are, but...the artists you’re referencing aren’t making remix stems available to the general public; remixers are getting label permissions, etc., subject to the artists approval.
I would be surprised if artists are just making stems available for the general public to mess around with, though in this day and age, maybe not TOO surprised.
I probably wouldn't be eager to do it just because I have lots of tracks that would have to be put into various stems, and it’d be time consuming just to go over all of the material again. I’ve got three years into this stuff! I need to give it a rest for awhile.