I kept pushing back on the RMA dept (who tried to get me to let them destroy the backplane lol), reopened a support case, and one particular support rep (Paul B) has been helping escalate internally. The backplane finally got to a "Systems PM" who may have actually resolved the issue, meaning...
Supermicro still has the backplane - waiting on them to ship it back - definitely going to try and recover it myself - thank you for the link! if i can't get that to work i'll post it up for sale with the disclaimers
Longshot, but looking for a bpn-sas3-846el1 or 846el2. Not interested in other models.
Long story short, firmware update gone bad and now supermicro says the expander chip is also bad and beyond repair, outside warranty window by 3 months.