New version designed with KiCad. Yet one more connector orientation. I might have been distracted and I left a hazard for SAM D21 compatibility. So I will respin this.
This revision has a more suitable RTC w/ a 6.8mm backup battery retainer on the bottom. I swapped out the hinged SD socket for a side-entry push-pull.
I'll release the schematic, layout, BOM, etc. after I've verified everything.