Suppose someone custom coded a custom designed expansion chip for the SNES. They submitted a patch that activates their custom chip, and submitted a custom emulator mod that can run the chip. Hacks patched with the custom chip would not run on console or on other emulators; only their own custom modified emulator. However, the chip also opens up a huge amount of possibilities for hacking. The chip heavily reduces slowdown, comes with almost no incompatibilities regarding tools and other patches, and allows a bunch of various added functions to enable a large amount of hacking possibilities, even more-so than either SA-1 or Super FX.
Hacks patched with the custom chip would not run on console
Working on real hardware is the standard we've chosen to enforce. If we accept hacks that need a custom emulator due to a custom chip, then we also have to accept hacks that need a custom emulator that happens to be ancient (aka accidentally - or intentionally - using emulator inaccuracies), or hacks that need the RVL-001 chip, and then we're not hacking SNES ROMs anymore and might as well switch to Unity3D.
-------------------- <blm> zsnes users are the flatearthers of emulation