Wersi, Lionstracs, and Korg are all producing instruments that meet most of your requirements. They all are software updateable, have great sounds, and aren't likely to be outdated around the corner. It's impossible to have a keyboard that is truly a vanguard product as these systems are designed years in advance to their release so technology will always be a bit behind in keyboard design. These instruments do represent the pinnacle as to what is available right now.

Korg is taking great strides to keep the Oasys software as up to date as possible. Lionstracs is also continually updating software and adding new features and bug fixes. Wersi isn't as quick to release software updates as they would much rather do one large update than release several smaller updates that may be buggy. I agree with that philosophy but it does make for longer periods before updates are available.

So far all three companies seem to listen to their end users and incorporate needed fixes and features in future OS updates. From personal experience I can tell you that Wersi's software is far more stable and bug free than either Lionstracs or the Korgs Oasys. I attest that to the fact Wersi only releases updates that they feel are relatively free of bugs and that Wersi were at the forefront of Open Ended Software instruments.

The main thing to consider is that these three companies do listen to their customers from what I've seen. The same can't be said for my past experiences with Yamaha. If Yamaha made the most advanced open ended keyboard to date with an upgradeable OS I'd run as far away as I could from it. Why you ask? Because their lack of support for OS on their other instruments was appalling. Of course YMMV greatly from mine.