I'm French so sorry for confusion.
It's my list of things that can be great if they were in SMBX.
1) Add Bowser as playable character.

2) Add the possibility to add NPC, without modifying the others.
3) Add the StarPower. The star power could be an event as the P Switch. The NPC could be the same as a SM64 star but with an option.
4) Add the possibility to set a time for a level (exemple : 1000s to finish 8-Final)
5) Add the possibility to change actual character with an event.
6) Add more NPC's (Snakes, SMB3 Sun, more Boss, etc)
7) When some NPCs (Bowser, Hammer Bro) are friendly, they attack you.
8) Add more tiles and scenery
9) Add a texture pack system (-> Minecraft) that does'nt affect custom textures of episodes, only unmodified textures.
10) Add the possibility to set the start life.
EDIT:
Send your Suggestions in this post if you want !