If no then are there any plans for multiplatform code in Wine?
NO! Even MacOSX specific code is not allowed
Is there an FAQ that explains why this is so?
I don't think this statement is accurate. The problem is "multiplatform" is ambiguous. If a "platform" is an operating system, multiplatform code is certainly allowed in Wine, though portable code is preferred to OS-specific code whenever possible. If a "platform" is a CPU, then with the exception of x86, assembly is not allowed, as there are so few non-x86 Windows binaries that this is essentially worthless. Similarly, the goal of Wine is _not_ to emulate the x86 CPU, so such emulation code is likewise not allowed in Wine. --Juan