I heard some old C seats would go into cargo jets as crew rest seats. Since they're largely mechanical I can see how they'd be easy to install on other aircraft. I guess no wiring is involved except for the massage feature, which UA disabled on 767s shortly before the conversion anyway...

During the previous refurb some old F seats went into the crew rest areas (eg 747 FA areas have old-style recliner F seats.) Not sure if there's any similar plans this time around, and it would just impact a handful of seats anyway.

I for one would love to buy an old seat Dunno what I'd do with it, but it'd sure be a lot of fun. If the UA Old Seat Manager reads this, PM me