D3 -> A3, what's next?
D3 was launched when high capacity ASIC for DASH released
A3 launched when ASIC for SiaCoin released
lets see whatever new ASIC comes, probably that would be X3 , where X= New ASIC Coin

Considering both Obelisk and Halong Mining are developing Decred miners, I would not be surprised if Bitmain was doing so as well.
Or they might go after the algorithms mineable by the Baikals. Who knows.
bitmain IS developing a decred asic right now, and I would absolutely bet on them beating obelisk + halong to market