It maybe fair comment that software technologies have not progressed as fast for a few years on OS4 and therefore emulation has closed the gap. However, this is now changing with Warp3D Nova and OpenGLES 2.0 being available on OS4. The power of the X5000, X1000 and a RadeonHD R7 or R9 card will really be put to good use with the advent of modern Shader 3D technology on AmigaOS. It will be a long time before WinUAE gets near that level, if it ever will.
Predicting WinUAE development is not my area of expertise, I was surprised it took so long for them to emulate PPC. When people are doing things for free then you can't really tell.
Emulating a radeon is likely to be harder than emulating a PPC, but the supported radeons are nearly 3 years old now. It will just take someone caring enough to put the work in.
It may be exciting hardware for amiga users, but it's trailing edge compared to other markets at the same price point.