Talked to a QC friend about the EU case yesterday, and he was of the opinion that, now the UK was no longer part of the EU jurisdiction, any judgement given out post Brexit would have to be referred to the Justice Ministry, who, politically, would be unlikely to allow it to proceed especially as the Supreme Court has already thrown out the basic complaint. Worst case would be that it is referred, by Government, to the Supreme Court, who, having already rejected similar claims by SISU, would almost certainly follow their previous rulings.
He did say that, havving in the past rejected similar claims about subsidies to sporting venues, that it would appear perverse if the EU did come down on the side of the SISU complaint. However as the EU investigation could be deemed to be "judged" by politicians rather than judges (although they do take legal advice) then it could be that "UK beating" might happen - but he feels it would be counterproductive for the EU to do this.