You must also take into consideration that WinUAE has been around for some time... In the beginning it was just another Useless Amiga Emulator, but with years of sweat and coding it has turned out to be as great as it is today. If a new emu comes around, don't expect it to do very much for some time. And when it actually gets useful to some extent, WinUAE will have gotten EVEN better. So I definitely feel the 'reinventing the wheel' argument to be a good point.
Of course, as I see it this guy wants to do it for fun and experience... So I don't say he shouldn't do it, I just say that you shouldn't expect it to be a justified competitor to WinUAE...