Take it with a grain of salt, but a rumor is going around that AMD's Navi GPU may feature eight streaming engines. While this would require significant changes to the front end, if it's true, it may solve one of the architectural deficiencies of the Polaris architecture. Potentially, this could also mean a doubling of the ROP units.
Five CUs spread across eight shader engines, assuming each CU continues to pack 64 stream processors, works out to 2,560 stream processors on the silicon. This arrangement is in stark contrast to the "Hawaii" silicon from 2013, which crammed 10 CUs per shader engine across four shader engines to achieve the same 2,560 SP count on the Radeon R9 290. The "Fiji" silicon that followed "Hawaii" stuck to the 4-shader engine arrangement.
While the rumor above should be taken with a healthy dose of skepticism, it does seem almost certainty that Navi will feature a 256-bit GDDR6 memory interface. This will enable a 50 to 75 percent higher memory bandwidth versus Polaris 30.