The more widely used packages should be moved to an official repository with review procedures. Perhaps the (quality) requirements can be lower, but these must be reviewed by trusted people.
The remaining packages should be moved to user namespaces, like the other user-package repos do. That will at least prevent (most) takeover attacks.
I think it should really be split into two parts:
@jpv2390@discuss.tchncs.de just below your comment, quoted the Arch wiki on the original purpose of the AUR.
Source
Thanks @jpv2390@discuss.tchncs.de