Agreed! All the applause goes to Mozilla for A-Frame and Jerome Etienne for AR.js, and I definitely agree they both play a major role in making AR much more approachable for us, Web developers.
As for ARCore, as far as I can tell, it is not currently supported on S7/S7 Edge, only on S8. However, S8+ and Note8 support is “coming soon”, as announced by Clay Bavor on twitter:
Perhaps if you reach out to Clay he could shed some light on their future plans for ARCore and their anticipated release schedule. Also, take a look at the following issue on GitHub for a list of devices that could potentially be supported down the road:
Update: Seems like S7 support is already here, according to this page. So if you edge an S7 device, I’d love to hear if the latest developer preview actually works for you.