Pretty sure they do, but I agree that adding `--firmware uefi` would be fine.
Yeah, we do try to maintain at least some back compat. Some things go through a deprecate-and-drop cycle, but that is more often driven by "the old thing is a pain to maintain internally" than by "the new thing is more user friendly".
New top level command line options are rare these days, and magic "do what I mean" options also rare: we tend to prefer "tell us specifically what you want".
But in this case, my suggestions should be fairly backwards compatible; retaining the default of BIOS but adding a simple `--firmware uefi` option would change nothing for existing users, and even defaulting to `--firmware uefi,bios` should be mostly compatible since it just tries UEFI and then promptly falls back to BIOS.