Front end that works with feeds from multiple sources, like RSS, and permits comments, posts etc using SSO, with all interactions logged centrally in the SSO account (for later edits deletes etc).
Sound about right?
Because you me it seems like every provider in that list should be able to make a profit off the data and interactions... With users who want increased privacy able to pay for an SSO subscription to prevent the sale of data on that end.
And we already have all the parts to make it work...