S9 will be in the market for a long time. If you are Bitmain, why would you want to release any new product when existing product still hit a 3 month ROI...
One reason may be to stay ahead, you don't want to find yourself 6 months from now in a position when a competitor is selling equipment you can't compete with. Also, there are players like Bitfury that may be eating part of Bitmains lunch in the industrial space.
What's news from Bitfury ?
I think Bitmain have a many money now to R&D, just check their new project Sophon.
Ultimately, to extend the life of the miner. I use Blissz firmware on an antminer D3. I can decrease the power consumption while keeping the hashing relatively high. He also solved the fan noise issue.
But nothing for S9....