That is definatly a possbility, if we get an X11 Server for Mac OS X Server.
The lastest version of WINE, includes an half decent CPU emulator, that allows WINE to run (if you want) on any archutechure. That means, for it should be a pretty easy port to Linux/PPC, once endianess / powerpc-only issues are fixed.
It should be noted, that WINE, when running on the CPU emulator is slower then WINE running on native x86 machine, since we know that emulators are slower then slow. The hope is that, when you are running the WIN32 calls / X11 calls in native PowerPC-format, that it will be faster then a completely emulated solution like BOCHs or VirtualPC/Softwindows.
For now, to run Windows apps on LinuxPPC, you can use BOCHs which completely emulates an x86 box. Another option is to use Mac-On-Linux, to run Mac OS 8.6 or 9.0 on LinuxPPC (in an seprate frame buffered console), which you use to run Windows apps. With SheepShaver, you'll be able to do this in an commerical package, also.
On Mac OS X, you are currently able to run VirtualPC/SoftWindows in the Mac OS 8.x box, on it.