First of all - don't use CC. It's outdated, buggy, and generally inferior.
C2 will revert back to canvas2D if webGL isn't supported, which does use software rendering. However, I believe you may have been misinformed about software rendering (At least in HTML5) as (I think) even when a computer has a weak graphics card, hardware rendering will always help, unless a graphics driver issue stops it.
Yeah, unfortunately C2 doesn't have much in terms of multiplayer ATM, however there are definitely some third party plugins you could check out.
Well I definitely need to check C2 out.
Hardware rendering absolutely is bad on old computers, because it puts so much if not all of the rendering for the gpu, which is just the case with CC if I understand correctly. I mean I haven't been able to get even a steady 60 fps on any of the examples I've downloaded for CC on my old laptop, but I get at least a steady 500 fps on anything I've made with mmf2, and the reason is that I have an integrated graphics card with only shared memory. I do have a desktop pc as well, and it has no problem what so ever, but I'd like my games to work on anything old or new :D Of course some of CC examples use effects and whatnot but I just don't need those. Actually the physics are the thing I'm interested in. And the light/shadow system.
I'm just installing C2, so I'll see how it works out (: