Name something innovative about CP88 other than being a ROMPler?
Why does the CP88 need to be innovative? It's a stage piano - the priorities should be on providing a good keyboard action, a good selection of sounds, and an intuitive interface.
If we compare the technology Yamaha has at hand, CP88 has less technology in it compared to CP4 and its high-end digital pianos. The "synthesis engine" is purely sample playback. This is somewhat questionable because the DP department takes a different approach and does add neat features to its higher-end digital pianos. P-515 is a really nice digital piano identical or better action and sounds better in my opinion.
My humble guess is Yamaha is trying to imitate Nord but they're short in budget. They cut down the features in their CP series and decreased the design complexity of releasing new sample libraries. Of course, the most important point is that they reduced the production and future support costs as it most likely uses the same engine as MONTAGE does. The only dynamic difference is the CP88 exclusive sample libraries, the rest are static, better action (compared to Montage8) and a different interface do not need any changes over time. Obviously, loading new samples on an instrument is an appealing concept, it makes users happy and makes them feel "satisfied" but the expressiveness of the instrument is questionable.
So the innovation is not user-oriented but profit oriented. This makes 100% sense for Yamaha but 0% to me. When I purchased my piano, I was looking for a complex instrument, not another AWM2 sample-playback keyboard.
Anyway, that's just my personal opinion. CP88 is a nice instrument. Great action and some neat samples. To me this is Yamaha's effort to fit the S90XX series into Nord's interface.
We can also ask the same question about Kawai/Korg/Roland etc: Why they put this much detail in their stage piano unlike Yamaha?