On your two points…
To the first point while I’ve not done that much with TrueDepth for facial mocap, I’ve done a fair amount with it for machine learning (trying to train a model to recognize emotion through expression), and based on spending (way, way, way) too much time in TrueDepth-generated data sets, I suspect the “plastic” issue is more an issue with how things utilize TrueDepth data and less the data itself.
The second, however, can be a legitimate problem, though it’s gotten a great deal better in more recent revisions of the iPhone. While gathering stuff for the ML training set (where a series of co-workers came through and did the various test expressions), we did have several iPhones and swapped them out periodically due to the thermal issue. (Now, we could have likely gone longer than we did before we strictly needed to do that, but we figured hey, no reason to push it.)
(Though now I’m a little curious myself how well the facial mocap works in practice rather than theory. Maybe tomorrow I’ll do a quick trial run of it! I’ve got both iClone and iPhone…)