I think C2 is a very good tool for game creation as it currently is. Of course there are still bugs to correct and some funcionalities it could have, but at the end of the day it's a game development tool and gets the job done.
To be honest C3 development idea at this point scares me a bit !
I dunno the business strategy Scirra has and if C3 development is "the way" to reach other markets and platforms -therefore audiences - but if that is the case, there are plenty of options out there to maintain C2 and generate revenue out of it.
I've worked with other engines and I've seen this path already. For instance:
1-GARAGE GAMES: They made TORQUE GAME ENGINE then they made TORQUE 3D. TORQUE GAME ENGINE felt incomplete as new features were added to TORQUE 3D. I think TORQUE 3D was a full rewrite (not sure).
2- THEGAMECREATORS: They made AGK 1 then they enhanced to AGK2 with crowdfunding a approache. The outcome...AGK 1 got updated to AGK 2 , AGK1 is still with issues and a new AGK2 is for sale with issues of its own as well...
What I'm trying to say here is that an engine development cycle is a very complex process not to say maintaining 2 engines! Even if Scirra gets more work power to the team I don't see C3 any time soon and I'm seeing it all over again...new bugs, new updates, etc.. and C2 being left behind with some things to address and left to oblivion.
If Scirra really thinks that is not possible to provide new features (regarding game making) into C2 then I think at least they should clean this product and define a point were they close it's development cycle. In my point of view (note that I don't know anything about C2 inner works) it seems that C2 hasn't reached its full potencial regarding game creation and funcionalities.
If Scirra just wants a new facelift and a new editor rewrite, well I think they could crowdfund it like THEGAMECREATORS did for their own editor. This is very different of rewriting an entire engine from scratch...
Just my two cents.
Regards !