Will telephoto ever be viable on NEX?

Anybody else confused why there are no teleconverters for e-mount (i.e., the type between body and lens, not attached to end of lens)? I'm not saying that they give great results, but I don't understand why Kenko or Tamron (if not Sony) don't at least offer them. Even if only mediocre, I'd think they would still sell enough to make it worth their while - I'd buy one.

I've tried 1.4X and 3X converters for Alpha-mount. While the 3X didn't work for me, I felt the 1.4X was OK for some situations. Maybe TC's are just a relic of the film days, and people think they get just as good results by cropping.