I can not rule it out from happening but that would be extremely unlikely from all the various emulator coding discussions I have seen.
At best you might get something extra or a feature they could never quite get working reliably (the DS kind of had the same limitations as the GBA in what it could emulate -- 8 bit and older just fine, 16 bit stuff pretty well at times but with serious limitations, however the DS was quite a bit more powerful and that extra power meant easier cheats, savestates, filters and such). Nobody is likely to have continued developing it in secret for their own personal use. You see that sort of thing occasionally on the PC but not for handhelds.
Most emulators were open source, or open source alternatives were since developed. If not then you might find that the authors feel enough time has passed.
If you wanted to try to collect all the emulators, snapshots of source code and get them all uploaded somewhere where you can easily link to things (I tried a bit with stuff on filetrip but not much and was more interested in source to non emulator homebrew when I did).