Hi Spiderpidge, sorry I only just saw your post here. I haven't tried the diet again beyond the 6 month first try and 3 month second try.
Since then I have found that cold / ice baths after exercise are able to stop me from having flare ups, although I have to do them every 2 days for about a week after any exercise to stop a flare up from happening. Also there are limits to the exercise I can do, squats in the gym seem off limits for example, and will cause me to flare up even with ice baths.
Personally I wasn't brave enough to try exercising (my trigger for SI / hip inflammation and pain flare ups) until I was 3 months into the diet - However it might have started working well before that time. Honestly if I were you I would stick with it and do it very strictly - that way you know if it can work for you or not, and that remission is at least possible by some means.
For me the diet remains an emergency option. I know that if the inflammation and pain ever becomes unmanageable by other means I can go on the diet at least. The degree to which my symptoms completely disappeared (both times I tried it)is still very shocking to me, nothing else has ever come close.
In the end I found the diet too monotonous, expensive, and anti-social to pursue long term, along with the fact it's obviously extreme and there may be health implications/imbalances from eating giant steaks every day

But as an AS sufferer you must know how terrible it is to be in pain all the time, and what that means for your life and health overall. Personally if forced by circumstance I would not be too upset about having to be on the diet, being pain free is just worth that much.
I know my response is 2 months late and I'm sure you've read the thread, but here are my tips for anyone else that's curious:
I made bone broth to drink at night when I couldn't sleep, due to my energy levels remaining high at night
Take a vitamin complex and eat some beef liver and other organ meats - vitamin levels on my bloods were totally normal when tested by my doc
Try and find a meat wholesaler / butcher to buy from, rather than supermarkets, much cheaper
You'll need to eat fatty cuts of meat to get enough calories, don't be afraid of it. Trying to eat 2-2500 calories a day of lean meat would be a nightmare
Would you mind sharing the reports you've seen of other people having success with the diet? Thanks!
Good luck with it and please report back on your progress