I was just coming here to post the same idea! When you're zoomed in on Field Maps (and out in the field) it can be hard to get a sense of scale (i.e. how zoomed in am i?!), a dynamic scale bar would be a huge help.
both would be great. I always found it curious there is no way to zoom to an absolute scale (and bonus points for 1"=40' type of zoom option dropdown) in the apps off the shelf. Particularly since the advent of vector basemaps several years ago, there is no need to hard-code levels of detail. Engineers etc want to see standard scales.
(sidenote: I've delved a bit down the geodesy rabbit hole before out of curiosity ... of course there are limits for broadscale apps i.e. what latitude is the scalebar is accurate, etc; but field collection is localized enough to negate that, particularly if in local project like state plane.)
