Using the Accountant addon, I've been keeping track of revenue from garrison missions since somewhere around March 2015. That was a few months before the first big garrison gold nerf. It was also a few months after I started keeping track before I had a 10 characters bringing in garrison gold. Also near the end of the expansion, my playtime dropped, so I wasn't anywhere close to maximizing gold missions.
Total Gold Revenue: 2,396,229
That's more gold than I've ever earned combined from Vanilla -> MoP, and it was all just from garrison missions.
