3way Link Exchange platform for Tube sites and adult blogs
 

I'm not sure if it already exists, so I ask :)

Why not build an adult version of one way link exchange platforms like this: iblbuilder.com

Value proposition:
adult blog / tube owners join the site for SE value
Heavy niche segmentation increases link quality
monetize via program ads and special offers/sponsorships

has the air of a google penalty about it.

That would definitely apply to TLA and other schemes but this seems to work differently. Besides, showing your url in a directory for such a scheme (same with very obvious behavior of some link sellers at forums) would be a bad move.

It can even be an "invisible" broker :) working primarily through email.

Another approach would be a completely DOUBLE BLIND system. This MIGHT prevent search engines from knowing the identities of the participants. Of course, there's several verification/marketing psychology issues with that approach. However, there's technical workarounds, I'm sure.