Many people agree that Legion is not an alt-friendly expansion. Weather its the rep, artifact knowledge, appearance unlocking, or simply not enough variety in leveling content, there is a lot to complain about.
Here are a few ideas i had to make it less of a grind.
-Artifact Knowledge: The idea I had for this is that for every character you get to max level, all your other characters get 1 free level of AK up to a max of 10. This will greatly increase the speed you can get into the max level content and greatly reduce the grind.
-Reputation: Blizzard doesn't want you to get to exalted too quickly so it would not work to make Rep. account bound. If it was, you could just do the emisonary quest on all characters and get exalted in just a few weeks. The way I think would work well to make it account bound, is to make it so that your alts are always one tier below you. If you get exalted, your alts will be 0/27000 Revered. If you are 13570/18000 Honored, your alts will be 0/9000 friendly. (I cannot remember if these are the correct numbers. I hope they are.) That way you can get your alts to exalted easier without letting you get exalted too fast.
-Leveling: Quite simply, for every character you get to max level, all other characters will get a 10% Xp increase for all Legion content, up to a max of 50%.
-Gear: To help you quickly get into Legion content for a small fee, I think that the Class hall armor should unlock account-wide.
-Appearance unlocking: I think a few of the appearances should unlock account-wide. The ones that should are the hidden ones (besides the 1st one of course), the pvp ones (again besides the first one), and the one for completing a dungeon with a 15+ keystone.
I feel with these changes, or some variant or amount of them, Legion could become a much more alt friendly expansion.
If you feel that some of the numbers are bad, or some of the ideas are just crap, let me know as I am curious what you think.
Also leave things you would do to make it better in the comments.