iOS devices can render Infinity Blade smoothly. I don't think few shapes (probably automatically cached as a bitmap) are going to be an issue.
And I don't get why Apple bothers with CgBi PNGs, since endian swap on ARM is a single cycle instruction, and it's probably free anyway while moving the bitmap to the GPU memory.
I don't think the Core Graphics vector stuff is in any way GPU accelerated, so the Infinity Blade comparison isn't appropriate.
The SoCs in iOS devices are shared-memory systems, so system memory is GPU memory.[1] But you're right, the endian swap could easily be done in the PNG decoder.
[1] I have to admit I'm not sure it's implemented as zero-copy through to userspace, though. The normal, 20-year-old GL texture APIs can certainly only be implemented via copying, and I'm not sure if OpenGL ES has anything like mappable texture pixel buffers. It would make a lot of sense though, considering how memory-starved embedded systems are.
And I don't get why Apple bothers with CgBi PNGs, since endian swap on ARM is a single cycle instruction, and it's probably free anyway while moving the bitmap to the GPU memory.