I think the most of the performance issues could be solved by offering us methods to load/unload assets & layouts at will and not just automatically by the engine itself.
In my opinion C2's current "dictatorship" with next to no control about the things mentioned above is a big mistake and I really hope, no I count on C3 to finally bring the right changes to this part of the engine.
Personally this is a key selling point for me and I honestly wouldn't consider purchasing C3, if it doesn't deliver any improvements for this.
Just as a side note, I think that C2 is currently the only game engine on the market that doesn't offer features like this.
(Please feel free to correct me if I'm wrong about this.)
I think it's due to a browser limitation. This has been requested many times and I really hope that this will be a thing in C3. I know that most projects won't need it, but there are some which do. Having a good automatic method to load/unload assets is a great thing, but having more control is always good. I also think that it would attract more developers.
I personally fully support Scirra in sticking to their guns (HTML5), focusing on whats important, and do it well (like they have been doing).
I can't agree more.
C2 has made some significant improvements in the past years (like Ashley listed them). I love the software, it's a pleasure to work and teach with it. I have to admit, I haven't gotten into iOS development yet, but I can't see any performance related problems in my projects on both PC and Android.