I'd say the chances of getting upgraded from a Little Mermaid room to a suite are close to zero. I'd think you'd be more likely to be moved to a different resort than upgrade from a standard room to a suite. It's cheaper to upgrade to a room at a moderate than to upgrade to a suite.
Anything is possible, but complimentary upgrades are not common, and upgrades from a standard room to a suite are really uncommon. Disney upgrades because of operational needs (an overbooked category, a maintenance issue, a block of rooms being refurbished), not just to fill an empty suite.