For me the FIA have put themselves in a difficult position. In reality any penalty should apply against the season the offence was committed in, but because they manipulated the outcome of the championship anyway, deducting points from Red Bull and its drivers would be a huge embarrassment for them.
They could deduct points this season and Red Bull would still comfortably win so they have a get out there, BUT whatever they do do is going to set a precedent so they really need to be careful what they do.