wouldn't touching the file in Lightroom or Adobe Camera raw and having it update the embedded preview be a work-around?
Not really. It would make for a really awkward workflow. PM is more of an upstream part of the workflow (injest, bulk metadata, rank & cull) rather than a downstream process (raw conversion, post processing, output, catalogue).
The way it is now PM forces the Windows-Leica(in-camera dng) user to do the ranking and culling in a separate application. I am not sure why a Windows-Leica user would buy PM unless they had other camera bodies that they were working with. I still think a WIC friendly PM is the way to go, particularly if Camera Bits hopes to widen their market with a cataloging module.
-- Mark --