I really dont see a big problem here. Adding new instructions will not hurt compatibility of existing software. Future software can make use of them but the programmer can also decide to leave them out and use standard instructions. I see it as added value and it can be used to show of the power of the new core and thus attract more users. It wasnt an uncommon thing in Amiga land to have different executables for different processors anyway. I dont expect to see that much new software anyway...
