I won't talk about the collaboration issue as I haven't been in a situation where I have needed to collaborate with anyone in C2, so I really don't have much experience with such matters.
However, I disagree with you on some counts regarding the proposed handling of the asset store.
Firstly, 2D art is much different to 3D art. I'm sure many serious 3D games use purchased stock models, however I've never heard of a serious 2D game that uses stock art. I suppose this is mainly because 2D art styles are extremely differentiated and recognizeable, and while 3D art can share these qualities in many cases, it's often more homogenous.
The other main asset store component is plugins, scripts and code snippets. I agree that these are important to many C2 games, however the community here has an extremely generous spirit and ATM gives all this stuff away for free. It would be difficult to start charging for code snippets when there's already such a rich base of code available for free.
You also mention that there are very few high profle games being made with C2. Ignoring the fact that C2 is primarily intended for beginners, I think this is more a factor of the tool's age than it's quality. Unity is so ething like 7 years old now so a comparison in that respect is hardly fair.
Just my 2c ;)