I have that Cthulhul Harn fanon filed in my hard drive - thanks. I do liberally mix Howard and Lovecraft, both in the Hyborian Age and in CoC.
Really, I think the problem is that I'm trying to find a replacement for Kethira because it isn't very well developed and I don't think that's going to change in the near future, if ever. That would be great if I wanted a more or less blank canvas that I could develop myself, but because of time constraints I'd like a more developed setting.
The Hyborian Age comes to mind because as I look at developing Kethira myself I start plugging in stereotypical earth cultures (Shorkyne = France, Trierzon = Spain, Dalkesh = Egypt, etc), which is what Howard did. The flavor is definitely different though.
I've also considered using Harn as a mythic Earth's Hy Brazil, say somewhere between 900 - 1200 AD. The problem with running it as a "lost island" is it then becomes very cut off from the rest of the world.