I may be completely wrong, but the tribunal only found that the APT rules were unlawful. So the question is whether they are null and void, and therefore unenforceable since inception and so any deals that were refused or modified can be waived through and unmodified (as City seem prefer for obvious reasons) or whether the rules just keep working with a few tweaks (as the PL is hoping). The proposed rule changes as reported by Keegan and Ziegler only relate to the APT rules, as well. Of course, I am wary of believing they understand the relevance of anything.
Still, the tribunal made no judgment on the lawfulness of the PSR rules, afaik, other than by inference (they obviously are for the treatment of shareholder loans, if that was unlawful for APT). Now, what does the PL do with those rules? If City's argument for APT prevails, then that means FFP/PSR would have been unlawful since inception in 2016 as well. That causes the PL lots of problems. And how shareholder loan interest is treated is the least of them.
We don't know if the tribunal has made a determination on how to proceed, do we? Keegan said the tribunal has been asked, which implies no answer yet. It seems to me that that is the big issue here, nothing else.