Animation of custom shapes seems like it would get into <canvas> territory. The canvas drawing API shares many commonalities with CoreGraphics[1], and I assume that CoreGragphics played some part in its design. A web developer should have no trouble transitioning to CoreGraphics (which, I will add, is not an Objective-C framework) in such a case.

[1] If you look at the browser-based Javascript implementation of CoreGraphics (http://cappuccino.org/learn/documentation/group__coregraphic...), many of the CG functions are just straight-up bridges to the local functions.