I think it’d be pretty cool at some point down the line.
Doesn’t have to be anything drastic, just a few layout configurations maybe, but mostly I’d like different enemies each time. It would also be a cool opportunity to have different named badasses show up each time, so people who aren’t really fans of savequit spamming to farm a single miniboss over and over (rather understandably so, imo) get a chance at the dedicated loot pool by playing something actually designed to be repeatable, a challenge for levelled characters, and played in co-op sessions.
Other games do this too (e.g. Destiny 2’s Dreaming City, Torchlight 2’s Mapworks, the Presequel’s Cortex Arena to a degree, even BL3’s own Cartel Mansion event). I know there’s been no mention of new Proving Grounds in the near future, and making the enemy waves have variations or be quasi-random is harder than scripting it, but I think it would be a huge boost.