Maybe that was the role of the camera in very early release, but it had changed a while back. The attention detection NN was added a long time ago (variables found way back in 2020), and since then, IR lights have been added and the latest version changed the angle so that the driver's hands could be seen.
A Tesla hacker has revealed what Tesla’s driver-facing camera in Model 3 and Model Y is looking for — hinting...
electrek.co
I'm not saying Elon wouldn't jump at it if NHTSA would allow hands free even without camera detection, but obviously they did not. I'm not sure if you were aware but NHTSA looked into it immediately after Elon made the tweet about releasing hands free mode. This is likely why it took so long for the feature to actually be released.
As for adding a dedicated camera, I find that extremely unlikely. Elon is on record as against "unnecessary" parts (see wiper detection, radar/USS removal, stalk removal, etc). They will likely just continually optimize the cabin camera for dual use. I was initially skeptical using the cabin camera would satisfy NHTSA, but unless they clamp down, looks like so far it is ok.
As for forum attitudes on camera based detection, although I am personally fine using the wheel nag system, I have said before that camera based detection is a better mechanism. The wheel nag complaints have been pretty long running here in the forums. Camera detection comes with its own trade-offs, but it may help address those complaints.
One can drive to the local Tesla SC and use their free wifi, which I have done a few times this year. But most times I don’t want to drive the 17 minutes to that facility because the final one km long access road to that facility also is the main feeder road for a huge gravel pit…and any...
teslamotorsclub.com