AK being account wide would go a long way towards solving the problem without diminishing the character progression of your main. We went through this with Garrisons in WoD, getting through all of it on multiple character was just a giant chore.
So far they're fixing it as they go to an extent. The Arcway, Court of Stars, and Karazhan are account-wide unlocks. Reps I think could use the MoP version of rep catch-up for alts and returning players, token purchasable from the faction vendor that doubles rep earned for that faction account-wide.