I just Googled it and supposedly the SFI2 visit does allow a co-op between ISP and Openreach.
However, as has been said already, it's not for FTTC.
SFI2 does allow the co-op IF the ISP selects it for another 20 quid or whatever it is wholesale rate. It makes sod all odds though, because BTO rely on the "Pair Quality Test" as the determining factor.
I've got a copper DSL service fault for a customer, it's never going to fail the PQT test unless they happen to be around at the exact moment it fails, and even then it's questionable as it doesn't last long. But it does kill the DSL service.
What's worse, is that I've discovered every other household on the route has the same issue, they've all raised faults at one time or another and the issue isn't resolved.
...because there's no mechanism to get BTO to fix a "general area" intermittent fault - if someone bulldozed the line plant, they'd fix it as a general issue (eventually), but this type of fault goes nowhere even WITH SFI2 fees paid.