Yes, it is a bass-specific option just for BIAB programming. It’s not a request for this to be notation. It’s no different a direction to BIAB than is ^D/C..bd which is also not notation.
For example, if I want to force a descending bass line I would like to be able to write D/F,D/E | D/D,D/C
Writing just D instead of D/D does not guarantee BIAB will play a D in the bass there.
I suppose what I find uncomfortable is that I see slash chords, at least in part, as an indication of a desired inversion rather than a specific direction to the bass player, though the bass player will normally follow that line anyway, so perhaps I'm being over picky.