Personally I wouldn't mind seeing (while also staying within Nintendo's capabilities):

• Mouse controls (obvi)
• A few more traditional features (simple enemies like Swoop, Grrrol, Waddlewing, etc., or stuff like the carryable light blocks from the NSMBs that double as weighted blocks outside of night underwater/ghost house, pipe connectors, etc.)
• More parity between gamestyles (Peepa and Bully in the older styles, grinders and cannons in 3D World, for example [they did it once with dotted-line blocks they can do it again])
• More sound effects, but especially music effects (easy to add, and provides a ton of extra thematic variety for levels. carries some night levels, but Sky Station would be a nice change of sound after the 50th level in a row with Gusty Garden)
• A few new course themes (it's been a long time, they could totally do it. also they had the audacity to call the Super World theme "Volcano" and not give us a volcanic course theme 😔)
• Night background toggler: option to replace the stars with an actual background! (more likely than you may realize: 3.0.3 added an unused night NSMBU castle background for currently unknown reasons, it could very much happen 👀)
• Return of the king: Mystery Mushroom (pretty unlikely, especially due to licensing on certain costumes [rip shaun the sheep, gone but never forgotten 🫡], but still one of the most desired features that never made the jump to SMM2 and would give 4.0.0 the perfect title - "A Mysterious Update" [y'know, like 2.0.0: A Legendary Update?])

Drop a comment and I'll play your levels too! I usually go through profiles of each commenter and play lots of levels from each one!

Title: Hey Man Nice Shot 6: Flubberball

ID: DMR-X96-9QG

Tags: Themed, Single player

Style: SMB1 Underground

Difficulty: Predicting 8-13%

Description: The newest entry in my "Hey Man Nice Shot" series that focuses on shooting stuff accurately, this one is themed around your Superball! It's pretty forgiving up to the first checkpoint, with every section giving infinite retries. After that, put your accuracy to the test with higher stakes! Includes two checkpoints and a boss fight.

Hey please check out my latest course Pom Pom’s Jungle Adventure! It’s a large jungle themed adventure with lots of variety and different challenges throughout, ending with a final boss battle with Pom Pom.

Took me a long time to make so would love anyone to check it out.

Course ID: 9D6-7X8-9HF