Immersionism is a strange beast, there have been many heated debates and disputes over it; if you want to read what others have been saying about it, just google it or go over to rpg.net or Story Games and search for the term...there's no end to discussion.
I think I might have accidentally stumbled upon something that makes me understand immersionism in my own specific, but possibly important way. I've come to this realization through the reading of the Sublime as understood by Longinus, the 1st century AD philosopher.
We might have been looking at immersionism all wrong, because of the term itself. We've been focusing on how a player is immersed in the game world.
Instead, we should have been looking at how the GM abducts the players into the world. It is through the sublime. "Immersionism" is a GM technique. Seen thus and not as "the absence of interruptions of flow" from the player's perspective, we might actually attempt contextualize its creative agenda...
Crazy talk, I know. I'll say more on the subject at a later date.