I am planning on writing a PSF player for the N64. I think that this, which is essentially a limited PSX emulator, is possible because the N64 enjoys the following advantages over the PSX:
And the best part is that the N64 and PSX have nearly compatible CPUs, possibly fully compatible. I might just be albe, with TLB exceptions, to capture writes and reads to PSX specific hardware, but leave the CPU grunt work to the CPU.

Of course the PSX is quite different from the N64, many elements of its hardware will have to be emulated in software on the N64. This includes the PSX sound hardware, the SPU, which is much more advanced than the N64's AI. Also I may need to handle any system functions the PSX's BIOS might provide.
I think it will be possible to emulate the SPU on the N64's RSP, one of the purposes of which is to generate audio.

It will be a big project and I have no idea when I will be able to start working on it, but here it is as a possibility.