It's very doubtful, actually more like not ever going to happen.
I've heard various numbers thrown around as far as the lifespan for the current fleet of Monorails and the shortest I have heard for any remote chance of replacement is at least 10 years.
So I think it would be safe to say that even if by some miracle they decided to replace the current fleet of 12 (or 11 depending on how you count them) in the next 5 years there would no doubt be a newer model of Monorail.
Also keep in mind that at WDW the monorail system is transportation, the one at DL is an attraction and is in no way even close to how the trains would need to be setup for WDW.
I believe, and this is just my opinion that when the time comes to replace the current fleet WDW will get trains custom built as close to the specs of these current ones so they do not have to worry about beam adjustments, platform modifications etc.