I always enjoyed Hey You! Pikachu, since the game seemed to have to many secrets and things left to discover. It's always made me a bit sad that it hasn't been emulatable due to the microphone, however, I thought through it a bit, and it seems like with a fairly small amount of effort, a usable HLE implementation could be made, that could end up even better than the original as far as Pikachu's ability to understand what you just said.
Looking at the last and only attempt to emulate the N64 Mic(forum.pj64-emu.com/showthread.php?t=3583), I decided that it's not worth trying to do an LLE implementation, mostly because I'm a complete novice in that area.
However, considering we have the list of phrases available in the game(pastebin.com/aG3rugAm), someone should be able to rapidly pull the matching digital responses for each phrase in the game(this may even already be listed in the ROM with the corresponding string, I couldn't manage to view the strings though). From there, a simple GUI could be made with buttons for key phrases allowing you to at least play the game.
Once that's done, you'd use one of the open-source speech-recognition softwares (en.wikipedia.org/wiki/List_of_speech_recognition_software#Open _source_acoustic_models_and_speech_corpu s) out there to pick up on the words and automatically send the correct digital command.
If that were in place, I think Pikachu may become more intelligent, it actually wouldn't be hard to add additional synonymous phrases that correspond to existing phrases to Pikachu's vocabulary, and you could even do translations to any language rapidly!
Also, for those interested, I put together a prototype of using a PC mic to detect the game's commands:
Hey You, Pikachu! Mic Test
So I went ahead and built a dictionary for Hey You! Pikachu using PocketSphinx, it works pretty well (about as well as the original game did). Needs some tweaking for commonly used words and Pokemon names (Pikachu is hit and miss), but otherwise it's actually quite good.
Run the batch file and say any of the in-game commands into your mic to see if it properly detects it.
I just need to look into tweaking the dictionary to be more precise for certain words and stop it from attempting to find more than one phrase used at once. Of course, still needing someone to find the VRU output for each phrase to pair it with this setup.