I'm not sold on this for multiple reasons:

1. It's very close to 5.15; I don't thing we should be making consequential UI changes to a controversial component three days before tagging.
2. Due to limitations of the current design, this will just exchange one problem (people can't see the pretty login screen wallpaper) for others (people get confused by the lack of a visible UI; people get frustrated by the UI disappearing before they've made a choice, etc.)
3. I'm not sure the "no controls are visible before user interaction" UI makes sense for a login screen. I tolerated it for the lock screen because there's only ever one user there, so immediately typing the password is a learnable habit, but the login screen incorporates a user switcher and there are more interactive possibilities. Furthermore, having there be basically no UI visible after you start up your computer just doesn't seem user-friendly to me. Sure, over time, people would get used to it, but is is really an improvement? I don't think so. GNOME has this type of design for their login screen and I find it really unfriendly and annoying there.

VDG's opinions these days are that the basic design needs to be looked at in the 5.16 timeframe, because with the current design we have no room to maneuver: every time we change one thing it regresses something else. That's a sign that the design isn't accommodating our needs anymore. See T10325: 5.16 Login screen improvements