In-game it looks like we'll have to wait next month to get the new rewards, but a recent tweet says:
"If you're setting out on the seas this weekend we want to know what you're planning. A spot of Emissary commerce trading? Are there Forts of Fortune in your future? Targeting the top of an Emissary Ledger for those new rewards? Tell us, we won't steal your loot. Maybe."
Does this means that if we are top 25% at the end of the current ledger we'll get the rewards?