I have a trip AUS -> FRA this coming Sunday. I just got an e-mail offering me to make an offer for an upgrade on the DFW/FRA segment. There's a slider that you move to select your offer, and the lowest I can submit is $550 and goes up to $1,200. The page where you submit the offer also shows a meter that indicates the "strength" of your offer. The "suggested" bid was $880.
The text of the invitation is:
We're excited to introduce a new service that lets you tell us how much an upgrade is worth to you. Simply make an offer and we will email you before check-in to let you know whether your offer was accepted.
Not every flight qualifies for this new option, but fortunately for you, your upcoming flight is eligible!
If you're interested in upgrading to Business, just click here and send us your offer. (Note, offer must be received no later than 48hrs prior to departure)
Thank you for flying with us, and we look forward to welcoming you on board soon.