I think Mercedes, Honda & Renault will want to keep the 1.6 V6T's until the end of the 2020 season as agreed as they have budgeted for them and would not want to shelve them so soon into the cycle.
I can see the fuel allowances being raised, the flow/mass could be raised from next season but an increase in fuel allowed may have to wait until 2017 as an increase to say 120-125kg lights-to-flag would require physically larger cars and the teams would require more time for this than next year.