I can also now report back. After a bit of a hassle in BKK at the transit desk (mostly to do with them being confused why I wanted to collect luggage in ZRH with the 15hr layover and re-check it in the next day) I swapped from 5D to 17K, so ended up with the throne. I have to say that this time (maybe because it was a dayflight and I wasn't trying so much to sleep) I found the seat better than the last time. It was still hard and not great if I wanted a full night's rest, and the footwell was tight, but not as tight as I remembered it.

As for when the seats opened, I have no idea - the app wouldn't let me check in so I had to do it at REP airport and there they were unable to call up the LX seatmap (it was a Thai Smile check-in desk). So I just went to the transit desk in BKK to ask, complete with my list of all the throne seats I had to literally go through every throne seat until the final one of 17K before they found an open seat. They didn't seem to be able to see themselves what was a throne and what was a window seat with another one next to it (to be fair, I think it's simply unfamiliarity of the Swiss layout among the staff at the LH group transit desk at BKK).

Funnily, when I got to the gate the gate agent asked me to change seat as 'somebody has booked 17K'. I told her I'd be happy to go back to my original 5D if that was the case, but I wouldn't exchange it for a seat with someone next to me at a window. I also told her I could upgrade with miles to First if they needed 17K. In the end, she kept me in 17K and the whole back row of business was empty, which was a nice bit of additional privacy. I used 17G to keep some stuff and have extra space around me in 17K.

I have to say, having flown LH A350 there and then LX 777 back, I vastly preferred LH in the middle aisle seat even to the LX throne. I didn't find the LH footsie problem many have mentioned and in general the soft product was a lot better on LH than LX. I was very disappointed that on LX for a 12hr flight they only had one meal service, followed by a barely edible chicken sandwich 2hrs before landing that they handed out in a plastic wrapper. They had a 'bistro' menu also before landing, but there wasn't much appetising on it. I had a burger, but when I asked for any sauce to put on it they didn't have any apart from mustard. In future I'll try to avoid LX on longhauls and stick with LH for the more comfortable seat and overall better service and catering (never thought I would say that).