I think that would be an AWESOME idea. And I think you could get it to work on LJ/DW - you're right that Tumblr doesn't allow for that kind of meme, and enough people still play on the kink meme that I think it'd be just a matter of advertising and prodding to get people to come play on LJ/DW, either with accounts or anon. There are still people playing over here - cherith and I have been pleasantly surprised at how many people are signing up for the Women of Dragon Age thing!

But Tumblr would be the place to advertise it, most definitely. The one thing that Tumblr is good for is getting a large number of people to see something in the shortest amount of time. :D