Didn't PMUA test something similar, but for Y, with the option to pre-order premium (believe these were C-style) meals. Think this was a test on certain flight, maybe some SFO TATL flights, IIRC. Don't know what the cost was.

I think TG does this for long-haul premium, too.

Will be interesting to see if they can get it right. They apparently can't even really keep special meal requests properly - my wife's request for a veggie meal for a longhaul wasn't even on the list, even though they most definitely had it down at somepoint, since NH got the memo without me having to separately request it (UA-issued ticket with TPAC segment on NH, intra-asia on UA).