I don't see the problems you project. Anandtech, on Nov14 said they are getting it for review- so other reviewers must be getting them as well:
https://www.anandtech.com/show/12038/ryzen-mobile-now-on-sale-hps-envy-x360- last sentence of the article.
And the chassi/cooling looks the same as used for Intel + MX150- but now cooling only APU:
http://apusilicon.com/hp-envy-x360-internals/
There is also plenty enough data on youtube and reddit: for example, here is a test of constant 40W power use:
https://www.youtube.com/watch?v=0A0YMY1bG30 . Users report good temperatures at constant high load (73C), and no throttling.
Also- this laptop is not only sold in US, but it appeared, in different configurations, for sale in Italy, Czech Republic, UK. Base configuration was sold out at Best Buy, but now is back on sale. That all does not look like bad shortage of units, or slow model not fit for reviews.