I like the idea. I think all new plugin owners should alert users of the new ownership. Some users won't care, but many will. The ones who don't care can simply ignore the message, much like they probably ignore all other messages in the admin area.

Mika's points are valid. I don't think the Plugin Review Team will be able to identify all ownership changes. But if WordPress core provided an easy, standardized way to communicate ownership change, that would encourage owners to use it.

I also think plugin developers should take responsibility here, and not place it on the Plugin Review Team. As plugin developers, if we transfer a plugin to another owner, it should be in the contract that the new owner must communicate the ownership change.

Taking it a step further, personally I would require the new owner to make a public announcement about the change, including a statement from me, as the previous owner. And if they have plans to make big changes, I would make sure those are communicated publicly as well. Especially data sharing or privacy-related changes.

I would also require them to announce the change as the first bullet point in the changelog.