The map that was released in a Miceage Update last winter shows an area for "Future Expansion" wedged between Toontown and Star Wars. It could easily be the location for a big show building for a Frozen ride, with the Arendelle village entrance built where the Fantasyland Theater now sits.
Like all the great E Tickets of the 20th century, the show building would sit beyond the railroad berm while the themed village/entrance would be inside the berm. Whether it's an expansion themed to Frozen or Oliver & Co. doesn't matter, the plan is obviously being built in to the Star Wars expansion next door.