Well its all in the title this feature exists for full games for quite some time now and i think its an great way to find your next game.
Why not enable this too for demos where you can browse demos in the same fashion?
Especially with these steam demo fests in mind where you can barely "consume" all stuff that is thrown at you.
But in the 4 months in between youre really starving on demos...
Maybe cause there are simply just few demos released in that time frame...
Or you simply cant find them so pretty please vote for an discovery list/feature for demos! :-)