C++ ruins it all
Development tools for the Newton are becoming more and more an issue - especially the C++ part of that problem. The NewtonScript side looks actually quite ok now with DyneTK, but we are still stuck with the ancient Norcroft C++ compiler for classic Mac OS (the 68k variant). Not that it won't work, but it makes moving to an Intel based Mac quite hard. Add to that the problem that serial ports don't seem to work here under BasiliskII and Mac OS X, it seems that you need a PowerPC or even 68k based Mac for any Newton C++ development.
I dug a bit deeper recently, but just to confirm that no version of GCC will ever be usable for C++ programming for the Newton. C will work, but the C++ code generated by GCC and the code in the Newton ROM won't play nicely due to vtable issues (among other things).
Well, one last straw still exists, although it is actually slightly insane to even consider this option: The Norcroft compiler is based on CFront, so theoretically, you could compile CFront and use it to convert C++ code into C code, which could then be compiled by e.g. GCC for the Newton. The old CFront sources are available, but a quick attempt at compiling them resulted in a bunch of errors... maybe it needs a bit more than just a quick attempt.