Very well put. Many airlines, AC for example, has been using PlusGrade for bid upgrade for years. It's not new.

UA's revenue management is dynamic, updated in real time based on time decay (as it gets closer to flight date) as well as inventory. Fare and upgrade cost is repriced in real time just as a equity derivative instrument. I'm sure they have considerations of other signals as well if data available: how often people with economy fares checking for upgrades, how often people are likely to bite for upgrade at which threshold on which route. UA's technology and interface design enables very dynamic and easy up sale push to customers, too.

With travel demand forecasted to be strong in 2024, I think you'll see more "buying tickets far far in advance" is cheaper to be less and less true. And entry and middle level "elite" statuses to become less and less valuable. For leisure travellers in premium cabin, the best way is to not beholden to one airlines but shop the cheapest business class fare with comparable products.