I love RCR, never could beat it. The most striking thing about this game is THERE IS SUCH A LARGE SELECTION OF FOOD ITEMS. So awesome that you can go to a diner, sushi bar, ice cream shop, supplements shop, stir fry joint, and each has an entirely unique menu, and the effects of the food subtly different. Pancakes give you like +20 health +1 defense whereas waffles give you +20 health +1 attack. There's definitely something going there, with potential for SaltW user custom shops, like Vellfire's Bento Bistro or JMickle's I don't really know what you eat.
The combat system is super zany, I think there's plenty of room for creativity there, even if you just re-sprite weapons and enemies. Depending on how customized the levels can be, I could easily imagine some Super Mario Bros. 2 type puzzles and levels, like carrying the key to the top of the stage while being chased by ghosts, giant radish pickups, parallel subterranean zones.
Graphics style is super simple and attractive for editting. I don't know if NES palette limitations would apply, would be nice to make it more colorful.