Since the VRC7 is a derivative of the OPL2 similar to the OPLL, we should be able to emulate the VRC7 on the OPL3 and OPL4.
Although the exact settings of the OPLL’s built-in instruments are not known yet, emulators contain pretty decent approximations which could be used. Once Wouter completes his research on the exact instrument ROM settings it can be updated to use the real values.
Note that the only VGM pack using the VRC7 is Lagrange Point and that one also uses the NES APU, which is an entirely different beast to emulate (don’t see that happening).
According to arfy Lagrange Point only uses the NES APU’s pulse channel (at 50%), the DPCM for drums, and triangle for a lone tom in track 16.
Oscilloscope view vid: https://youtu.be/yJahVleP1M8
Another use case: creating music with tools like FamiTracker which use both VRC7 and 5B (essentially the same as the MSX PSG).