Shouldn't leveling be more fun?
New players would be more compelled to play and creating alts wouldn't feel like such a chore.
But to make leveling fun again, they'd need to make it take more time to reach level cap so there's a player stagnation at any level stage to create actual multiplayer interaction (Please LFD doesn't qualify as multiplayer in my book) and make leveling more challenging (harder quests/dungeons and forcing players to travel around the world to break the current linear questing style)
But then veteran players would complain because endgame content (where the ''real'' game is all at) takes more time to reach, and every extra minutes taken to level up a character is an additionnal wasted minute.
But how to make leveling relevent both for new players and veterans? I played Diablo 3 recently and while it might be one of the worst exemple for a leveling system, i feel like they took ONE step in the right direction. Legendary items you can can be dismantled to extract their unique property and be used later. It might not be much, but at least it made it feel like my character was actualy progressing and becoming more powerful.
Now can't they expand over that system? They could make universal currencies/armor, so time spent leveling doesn't feel like it is being wasted. Give more currencies in dungeons and get rid of LFD so veterans creating an alt will actively seek for players to group, which in turns make multiplayer more accessible for new players. Allow items to be dismantled for currencies. Give even more currencies when experiencing a low-level dungeon/raid for the first time, so leveling players would feel compelled to play ALL old content (you know, instead of letting all the old content take the dust, give players a reason to go back) Once reaching level cap players can buy gear or vanity items with said currency. It would justify increasing the amount of time it takes leveling.
Two birds one stone. Satisfy both new and veteran players by giving a fun, engaging and rewarding leveling experience.