Can you justify why you need that at all? The other reason we omitted lumens is that there’s doesn’t seem to be any need for it; even if every device reported lumens correctly, there’s really no reason to have light-level information at the lumen granularity. The three categories we defined seem to capture all that you need to actually respond to - normal light, low light, and bright light. There just isn’t anything you can usefully adjust at a higher granularity than that.
(It also means you don’t have to go research what lumen levels actually mean, since I doubt very many people know off the top of their head how bright 1000 lumens are. ^_^)
The problems with viewing distance are separate, and have already been discussed - viewing distance just isn’t a useful thing to ask about. It’s being used as a proxy for a few other types of things, and if we want to address those, we should do so directly. Using indirect variables just means you’ll react incorrectly when the things you’re measuring don’t perfectly correspond to the things you’re trying to respond to.
In particular, “far” viewing distance is really just a proxy for “probably interacting more passively” - it’s a user interaction mode you’re trying to detect/respond to, not the distance from the screen.