This has me wondering...what's the yield-per-space on the planes in F vs W vs Y? I wonder because (this may sound a bit counter-intuitive) if they're selling 3/4 of F space on a regular basis (and this is including both smaller destinations with very little demand for F as well as awkward-hour flights that don't sell much, either) and space is constrained, if the yields in F are ahead of Y, whether we might not see some enlargement of F on some planes? My thinking is that if it might be a little bit tricky to push fares up in Y, it might be easier to shrink Y (if they're selling most/all of F as-is) and reduce the number of "cheap seats" being sold, and expand F/W if the latter can yield more on a per-space basis.

[Note: I do not expect this to be done with an eye towards there being more UG space as such; depending on relative yields it might just make more sense to add premium cabin capacity on some of the larger narrow-body planes if they can sell most/all of the space on a regular basis as-is.]