I guess that choosing to use they/them pronouns is not only about leaving them space to decide what they will be eventually more comfortable using what.

I guess it is also about education, as they would normalize/respect people and their pronouns. Of course, there are other methods to teach basic respect to a child. However, I believe I'd be personally more comfortable being only a child instead of following a script of how should I behave according to my birth genitals. Then they/them would be a weight less to a child lift.

So, it seems quite nice to be raised as you suggested, I'd had loved it if I was raised like this. Hope it was helpful (btw, I'm a cis women)