Recently I was looking at the OSIS project on the nocrew site (osis.nocrew.org). It seems to be something like what you are talking about in your post. It includes emulators for the individual parts of tos. It is written to run on top of the Linux kernal. Therefore they include a 68k emulator for those who are running x86 linux. For those running 68klinux .. the 68k emulator of course is not needed.
I guess it is written in C (at least the m68k emulator anyway) and therefore the compiler is most likely GCC. So.. this would appear to be very cross platform... any platform that can run linux (which is all the major ones and a lot of the minor ones) should be able to run this. This looks really good.. however I can't speak from experience as I haven't gone to the effort to try this out yet.. and its still not finished.
One thing I would like to know about OSIS however is whether it will allow compiled applications to run in the native processors machine code... or whether all of the emulated components depend on the 68k emulator being there? (maybe someone can help with this) or if only the running application requires the emulator? I think if we are to graduate to new processors we need native non-68k gem applications to be able to be compiled and run in addition to the original ones being run through an emulator.
As for the comment of programming only gem calls in a high level language instead of hitting the hardware directly with assembly calls... I think this is a must for any practical OS these days. Prior to the days of good 3d Graphics cards being available for the PC games programmers continued to write games directly for MSDOS rather that accept the amount of processing power that windows chewed up. These days of Nvidias and other 3d graphics processors however it would mean that if they were to continue programming for MSDOS directly... they would need to include 3d graphics card device driver code in their programs... and this is no longer practical... Its far more practical to leave that to windows.. accept the drop in available power as a result and use directx to take advantage of the new graphic processors power.
Anyway regardless of the above.. multitasking systems are always going to have problems with software that hits the hardware directly... so its basically a no no these days. And I'm pretty sure that multitasking is where we all want to be these days :)
