Before loads approached 100%, UA used to guarantee GS & 1K paying full Y a seat up to T-24. Practically speaking, UA would overbook by one more on most flights at any time for full Y. This barely moved the IDB needle and even if UA had to shell out IDB once in a great while, it more than made up for that payout with the happy HVC.
The technology here is not quite so easy and while the concept has made sense for a long time, the execution has not been easy.
Using real people to call and engage in negotiations is time-consuming and expensive. This is not people intensive, the deal is the deal, and if UA has satisfied its needs by the time you respond, well you're too late.
Nothing will ever totally replace the VDB at the gate, but this, if it is properly executed, will go a long way. A side benefit is that it contributes to an ontime push and fewer frustrating waits on arriving aircraft with too many aircraft stuck at the gate.