After seeing the results of the ROA changes at DLR, I would love to see what they could do with ROA at WDW, for both the riverboat view and the railroad view. Add some extra, more expansive scenes with AAs along the river, and maybe even indoor portions for the railroad similar to the dioramas at DLR (but not carbon copies of what they have at DL). Even if they shortened the river by digging a path through the larger northern half of TSI to act as the bend in the river that currently sits at the far north end of TSI, I would be OK with it, as long as they effectively utilized the extra space created by closing off the current north riverbend/northern TSI. (see extremely crude pic below)The Liberty Belle and the Railroad are two massive E-tickets waiting to happen. All it would take are a few pennies, peanuts compared to the billion dollar lands they're building.
On top of that they both add class, a classic Disney vibe, and beautiful park visuals.
The main issue with the riverboat is the journey is too long for modern attention spans. Halve the size of the loop, and build out frontierland and Liberty Square to make capacity, restaurants, maybe add another attraction or two.
This would help balance the Tomorrowland and Fantasyland expansions, without necessarilly increasing demand significantly.