Why are Red Bull suddenly interested in working with Renault again? The trouble started with an assumption that they would develop their own power unit and leave Red Bull high and dry. Changes to the regs for next year could mean teams wouldn't be able to subsidise the cost of developing a new engine by flogging old ones to back markers.
And Red Bull.
From Formula 1 Blog:
"One of the issues is this ability to run a year-old unit, which Manor is doing now and Toro Rosso might like to do with Ferrari in 2016, and this is now seemingly a loop-hole that has been closed."
It seems like the FIA is trying to punish teams who only want to supply engines to teams that don't pose a threat. I'd assume that, to keep everyone happy, they'll enforce a rule change that ensures teams must supply the same engines they use and only make exceptions for less affluent operations.