I support adding something like this on textarea. It’s not clear to me that it should be a CSS feature though. I think an attribute on textarea would make more sense to me since this is really just trying to fix that textarea has some special sizing rules. I also think an attribute on textarea is more discoverable.
In either case, I don’t feel strongly about the color we paint the bikeshed, so I’d easily be swayed if other browser vendors felt differently or if there was a strong web developer sentiment for a particular solution.