I have subbed (mainly on the basis of my experience with C2) but I have not transferred to working in it because it is still beta and subject to issues, bugs, crashes.
Personally I wouldn't recommend anyone to transfer any projects, especially large ones, into beta software. There is a continual risk of loosing work or a project file becoming corrupted. I will probably even wait some further months after full release before venturing in just to ensure as much stability as possible.
However the fact that it runs in a browser , that it has an additional mobile UI that allows me to comfortably develop on my phone, that from the same phone I can perform a cloud build or a remote preview. This is the sort tech that makes C3 "quietly revolutionary".
Yesterday I went to c3 website on my phone, opened C3, opened my C2 project file from google drive, demoed my game to 2 people in the office at the same time using C3 (note I not using c3 for development yet just stuff like this). They were able to play it on their phones while I hosted it on my phone. Suffice to say that they were both more impressed with this C3 tech than the game itself.
I have also noticed that games being previewed on C3 are performing better than when hosted with C2 especially on crappier mobile devices.(I understand it is using the same run time but something has definitely changed behind the scenes maybe its just a preview thing I don't know)
So no , not yet, but soon....