Hi Jonathan!
(pinging Martin Roth who is currently messing around with Pd and web audio as well)
Yes I am pretty sure it does implement subpatches.
As for copy/paste that's another problem. I have never seen something such as copy/pasting graphical objects from one html page to another ... but nothing's impossible!!!
Something I am more concerned about is the ability to create controls (buttons, number boxes, ...). I think it wasn't really designed for this purpose.
On the other hand, even if the whole UI ends up not being a good match, several of it's components (for example auto layout, and so on) have been released as separate open-source packages so a possibility would be to build on top of those.
In the next few weeks, I'll be finalizing WebPd refactor to Web Audio, and then if you want we can keep in touch and in sync to test this noflo UI in a pd context!