it would be really cool for MESS to up the accuracy ante on Nintendo consoles by actually emulating the lockout ICs. They are in fact microcontrollers, after all. It would also be very helpful for the N64, since the IPL does some handshaking with the lockout ICs. Not only that, the IC that handles peripheral I/O on the N64 is theorized to be a microcontroller - it also supplies the 2k or so IPL ROM, so it would be nice to get that torched and read as well.
The lockout chips have all been decapped and imaged from what I recall. The ROM bits for the NES lockout chips have been around for 7 or 8 years. The ROM/info for the "rabbit" (tengen's clone) is out there too. I traced out the die schematic for this part quite a few years ago.
the lockout chips on the NES/SNES wouldn't help to increase accuracy (unless you want to simulate the annoyance of a blinking power light and screen flashing) though it would help on the N64.