Is there any indication that UA is offering point of sale upsell fares for longer flights (4+ hours) where the difference between first and E+ is more of an issue?

From my perspective as a 1P with many 500 mile certs, the difference between first and E+ on short flights is so negligble that I don't bother to try to upgrade even if space is available; I'd rather let the certs roll over into miles than use them on a short flight. (In fact, I actually prefer E+ to many F bulkheads.) So if UA is converting F seats into cash on these flights, good for them.

However, I think its a different story if UA is selling cheap upgrades on longer domestic flights or on international flights. I save my certs for use on long 2 class domestic flights, and would hate to see availability disappear. And on international flights, I see the single best benefit of miles as the ability to upgrade to C; I would hate to see upgrade inventory disappear.