I personally wish for this land to be equivalent to how Tron feels for Tomorrowland. It doesn't have to be scary perhaps, but Tron is definitely a significant step-up in intensity and grounding compared to offerings like Cosmic Rays and Laugh Floor towards the front of the land. The Maleficent coaster could be like that: an addition to the larger Fantasyland area for older kids who've already conquered Space Mountain. Acting similar to an Everest, Tron, or hopefully even Hagrid's. I do think Magic Kingdom has an open spot for a ride like that still.
I think a dark ride going through a number of rooms featuring iconic Disney Villains makes a lot of sense too. They would be able to represent a great amount of the Villain cast in a singular big project. And more importantly, it allows a lot more opportunity to be both a little dangerous and significantly more whimsical. Like the in-between step of Spider-Man and Unchained - dangerous villains coming after you from every corner, but still having that necessary level of camp and comedy that makes these villains engaging in the first place. "Things are starting to heat up!" and "Happy landings!"-type vibe.
That's why I'm not quite sure why a Maleficent boat ride would be the move - in any plan, honestly. Maleficent can have some good fun, but she's also often serious business. She's portrayed as the head honcho of the group for a reason: she's both the lead tactition, with the potential strength of an enforcer. She's camp, but all of that is clearly just barely covering up incredible malevolence backed by significant power. It makes sense to save her for the thrill ride, where a limited amount of Ghost Host-type quips could effectively show off her characterization. I have no idea what we'd be doing for the extent of an entire slow-paced boat attraction starring her. Is she giving a tour of her castle? Why limit this to only her?