Thanks for your reply :) I've spent today crashing everything in sight trying to get access to the camera texture in the current QCAR sdk (2.0.31).
I've tried building a new test project, using your old cube one, and the sdk's current background camera texture example and all I get is crashes trying to use their call to bind the internal camera texture using QCAR::Renderer::getInstance().bindVideoBackground(0). I've read on the Vuforia forums that it binds the texture and sets an internal shader, but even trying to clean up the OpenGL state I manage to crash things or end up with OpenGL 0x0502 errors. I couldn't really pinpoint it, but it would fail after using that call once. I've also tried to compare the various CCGLView vs AR_EAGL views to see what might be different, but it's hard work.
I also tried various threading workarounds as well, to avoid the internal QCAR thread which updates the texture clashing with the cocos DisplayLink thread. I stopped the animation and hooked the scene draw to the renderFrameQCAR call on the OpenGL view, which stopped my early OpenGL crashes but didn't help with the bindVideoBackground(0) calls. Before anyone asks, yes, the Vuforia BackgroundTextureAccess sample runs fine on my phone, so there's something going on trying to drop the basic QCAR startup/camera background into a skeleton cocos2d project.
I've just got a slightly faster camera pixels->texture going which doesn't use your cube demo's method of converting the pixel data to a UIImage and then creating a texture from it each frame. Instead, it creates the texture once and then updates it after that. It's working in RGB888 using the default camera size (480x360) at 60fps on my iPhone 4s. If I get it going bigger and better I'll post up the code soon.