There's a lot of negativity surrounding the one-app-a-time change. Sensible.
But I actually predict this is necessary for Autopilot visibility/safety. Its been no secret that Autopilot will be heavily reliant on nav for more autonomy (from leaks to Elon's own remarks). I think at some point the navigation UI will have to include information encoding (via colors, text, whatever) of where Autopilot can be used "hands free", "eyes free", and likely other information. (completely ignoring whether this hardware is even capable, let's just talk theoretically).
I think this change is moving towards that: they'll surface more important information on the nav (hopefully in addition to the IC, since that's safer) and they want to make sure users always have the nav visible.
I totally get that looking at the center media is not super safe, but I think they'll want to show it anyways.
Also, there are definitely arguments of "yeah but you could use popups" or "but only show the nav w/ AP on then" and so on. There are tons of UX ideas that can be adopted that are probably viable against "show the nav all the time". I get it. I'm just offering up and opinion on why this change might be important.