Is there a way to do that now? If not, is this ability coming soon?
No, and nobody who knows is allowed to say.
So. I've done a lot of reading since last night, including some papers from the Metadata Working Group.
Here's what I think I've learned:
the feature I want, that I've been calling "face tagging", is called "Image Region Metadata" by software companies
Adobe created support for image region metadata within XMP
Adobe, Apple, Canon, Microsoft, Nokia and Sony founded something called the Metadata Working Group to standardize the use of increasingly complex metadata
The Metadata Working Group published a set of guidelines in Nov 2010 that included guidelines for image region metadata
As of now, only Google Picasa and Windows Photo Gallery actually support any kind of XMP image region metadata (or what I called "face tagging")
Did I get all that correct?
Your summary of the Metadata Working Group is correct. You might add your vote and opinions to these topics in the official Adobe feedback forum: