I think large data broker businesses are going to have a hard time integrating federated sources with their existing user data. Mainly because, they have privacy policies that let them sell their user's data, retain it, monetise it and overall take ownership of it. Everyone that signs up to any of the bigger social media sites agrees to that.
But the user's whose data they will be vacuuming up by joining federated instances will not have agreed to any such privacy policy and as such could create a need to at least separate data.
I'm not a legal expert, but I'm sure there's a reason for these long and convoluted privacy policies and I find it hard to believe they work in the user's favour.