The reason we've avoided registering "Cinnamon" as a desktop name is that it opens up issues with many upstream apps that currently OnlyShowIn=Gnome or Gnome;Unity or just Unity. The relationship Mint has with Gnome and Ubuntu isn't genial enough that we could get them to add Cinnamon to their desktop files, so we would have to distribute and maintain separate duplicate .desktop files just for Cinnamon for these upstream packages.