What a great read! Thank you for writing it, it must've taken a lot of time to research and write this piece!
I'm currently letting your theory sink in a bit. I don't know if it's the full thruth and nothing but the truth, but I do think it's on the level that Ron Gilbert operates on. He's a big fan of David Lynch and the layered narrative structure he (often unconsiously) uses in his work. Monkey Island has obviously always been a deeply personal project for Ron, which is showcased by his constant willingness to return to the franchise over the course of 30 years. I'd like to think that that's because of a deeper layer like the one you described.
Anyway, the thought that there could be so much thought put into this game is really mind boggling... and it really makes me want to play Return again just to see if your theory matches up.
I'd like to add a log to your fire: In the years that Ron couldn't make a Monkey Island game, he supposedly gave this description about a possible third Monkey Island game, "It takes place in hell and Stan is involved." Looking at you're theory, you might want to let the last part of that sentence sink in... seems to match up.
Thanks for the read! It kept me off work for way too long! π