A lot of people set their avatar height as their real height. This is incorrect: Avatar height is actually the height of the viewpoint, not the height of the top of the head (it should be renamed to eye height or viewpoint height).

Real Height Mode would remove this uncertainty and just scale everyone appropriately to their actual heights.

There is a problem with vrchat beta

This would be good for specific gamemodes where bigger avatars have a clear advantage and where movements and actions that are 1to1 with reality are wanted. Although it doesn't have to be tracked by FBT. So long as the scale of the camera is 1.00 a real meter will be a game meter. But then the issue is the avatar proportions. With off proportions your real feet will be below or above the ground. I think it would be sorta pointless to have a button to set real height only for you to be bigger or smaller because of off proportions.

Before I read the post details I thought you were requesting the ability to set world instances to a real world height mode. I think that would be a hilarious feature that I hope some udon creators apply. To walk around publics and see all users as their correct height sounds like a fun world toggle.

Take my upvote anyway as this sounds useful. Maybe one day we could proportion our avatar bone lengths in game and this real world button would be far more useful as well.

I do think that's a wonderful idea, the value / math to get your real size already exist (for FBT at least) ; it would be a good implementation for VRC !