it would be good to be able to put different icons on the different desktops, that way one could have one desktop for every activity (work, play, ..), each one with the files, folders, links you need

this should be also simply enough to do: making a desktop folder per each desktop should work
better, this could be an added feature: leaving all as is (only one ~/Desktop folder), but adding in it for each file an optional hidden config file that tells on which desktops it should appear: when drawing the desktop, the sw reads the file and knows whether it must draw the icon or not; for links, it's even easier because it could be just an additional entry in the link file, and on option "show on desktop 1/2/.../all" in the link creator

i think this feature would be helpful for a lot of people who now solves the problem by making defferent users for the different needs, which obviously requires more work and makes you lose the advantages of multiple desktops