Noting the comments above I've dug further into the BA scheme and it seems the QR, AA and QF legs will remain on a distance basis. (Some wildly different numbers are coming back from their Avios calculator so we will have to see what actually happens though.)

Seems like an incentive for BA frequent flyer to avoid BA, which is presumably not their intention. I guess they are hoping that all the OW airlines move to price based models which would be a shame.