Loving these ideas and all the hype towards Yooka-Laylee. I myself am very excited and can't wait to see what else Playtonic Games has to offer in the future but most importantly, Yooka-Laylee.
Here are my ideas:
1. As Laylee is a bat, make a reference to Ozzy Osbourne biting the head of a bat of which he thought was a Halloween decoration. It'd be hilarious and I think the best way to make this reference is to have a large character like a bear or a standing crocodile or something else with sharp teeth or in resemblance to Ozzy to bite off Laylee's head and then it grows back or to make some sort of joke about it.
2. Seeing as there are day and night transitions, maybe Yooka and/or Laylee can obtain night vision goggles at some point to be able to see through the darkness or there can be some sort of creatures with lights on them, illuminating paths or flying above and the light from their bodies or some sort of beacon radiates downwards to the surface/ground or around the area to light it up. It would be weird if street light-esque objects were seen in a jungle world! But if you want that obscurity, then go for it. Maybe there could be something related to tribal events at night or a minigame and/or cutscene where Yooka and Laylee are tied to a post haha and are a part of some tribal ritual with animals or creatures that look like tribesmen and tribeswomen.
3. A city world which is an open-world environment of course. Scaling buildings can be a thing, maybe parachuting, going into buildings and talking to animal executive and corporate workers for a certain mission or homeless animals who give you hints or have something interesting or funny to say about the place and/or their life. Maybe there can be stalls where Yooka and Laylee can purchase certain items (if you're into adding RPG elements into Yooka-Laylee). Minigames within the city such as a paper tossing game in an office, a street race, parachuting collecting Pagies.
4. Yooka can use his long tongue as part of a moveset to eat enemies (like huge flies) or collect certain items from a distance. Maybe it can also be used to latch onto objects and spin him around.
5. An underwater world possibly but I don't know if Yooka and Laylee would be suited to it. It'd be cool nonetheless because they can travel through pipes and reach caverns that have no water and can be walked around and the duo will be able to use their moves as they would above the water on land. They should be able to talk to sharks, fish, octopi, maybe seahorses and any other marine life that seem quirky and interesting.
6. In the Jungle world, maybe there can be some sort of white water rafting/river rapid minigame which could be really fun and challenging, giving a reward at the end. It'd use a blow-up water raft thing (one you sit in to go down the rapids in like an oval shape) and you'd knock into rocks which will maybe take you back to the start or there'd be a time limit and you can set high scores.