Theoretically you could get the PPC version of Blitz for your Intel Mac, force the hack built into BMK to determine whether it's a PPC system or an Intel system and then use it to build PPC binaries. I suppose I should try it at some point because I don't see why it wouldn't work.
For it to be simple and built in would kinda complicate the way Max works right now, because you'd need to keep two sets of the mods in the same places, etc. It should be doable though.
For cross-compiling other platforms, it is again theoretically doable, but complicates the build environment even further. You'd need a full crosscompiling GCC suite, full headers for each OS, plus libraries used for linking, etc.
For it to be simple and built in would kinda complicate the way Max works right now, because you'd need to keep two sets of the mods in the same places, etc. It should be doable though.
For cross-compiling other platforms, it is again theoretically doable, but complicates the build environment even further. You'd need a full crosscompiling GCC suite, full headers for each OS, plus libraries used for linking, etc.