You are describing a ursa mini pro, which you already own
BMD cameras offer incredible value but they must consider cannibalisation when deciding features.
The pockets already have an incredible list of features for the price, XLR, Prores, Timecode, Raw recording, 5inch screen, EVF,ND's it's insane.
Sure SDI would be a nice to have, not sure about the logistics of swappable mounts. I mean the 4k can be already be adapted to pretty much any mount...