I can somewhat understand why it isn't already a platform, (vagueness of publisher/developer information, lack of box art, etc.) however these same problems can also apply to both iOS and Android, which *are* included as platforms already. On top of that, the sheer number of games released for Flash and the fact that it's been around for quite a while (and was even considered ubiquitous in the mid-2000s) should be indication that it's more than notable enough to earn it's own platform category.
Oh, and PS: this is my first post here, so if this ends up being the wrong place to post platform requests, my apalogies.
If you have a new public project, please provide a link to it so we can highlight cool new applications!