seat-tube is square. do think the few people i've seen with gravel bikes and mtb di2 2x i've seen have all had band-on clamps which obviously work fine. i was just hoping there was some direct mount adapter type thing someone had made. doesn't seem to be though.
The number of people using 2x MTB groupsets will be fairly small these days and the number of people wanting to put it on a gravel bike, even fewer.
Just run 1x?
Trim the braze on from the frame and run a band on adapter?