Forgive me, but can we all stop calling it an 'overlay'? It's not an overlay (that's what happens when the Jungle Cruise becomes the Jingle Cruise). What we're talking about is a re-theme.
Having said that, I agree that a re-theme of the original maestrom attraction is likely the course to be taken here.... but how are they going to 'reverse' it without gutting/removing the climb mechanism and retrofitting it where the drop exists? At that point, it might serve to gut the whole ride system and start over. To me that seems like a great deal of work with very little actual benefit. You speak of cheap solutions, but a reversal of the track is anything but. Personally, I think that portion of the rumor has got about as much chance of happening as a 5th gate.
Having gotten that off my chest, I have to say a 'boat ride' themed to frozen makes stupid sense. In the movie, every single boat or ship got literally frozen in the fjord and/or crushed in the ice. So how is flowing water in the frozen land of Arendale going to make much sense in the story line of such an attraction. I don't get it.
I also agree that the potential increase in ride interest will turn the Norway pavilion into a veritable traffic ridden nightmare. I seriously hold out hope that they slap in a quick and dirty omnimover and increase the capacity of this attraction a bit....or else the east side of the WS is going to have to be avoided at all costs.
There goes my frequent tequila stops at La Cava