I just bought Bitwig and am going through the manual. In my eyes it's a fantastically designed DAW and is going big places. It's great to work with a beautiful modern looking program without the bloat and legacy of Sonar. You cannot underestimate the significance of it being such a young DAW - all DAW's started with a much smaller feature set than they ended up with, and there's always going to be a certain amount of feeling around before they get things 100% right.
It will probably end up with REX support, and will also probably end up with decent time stretching. For now, it doesn't bother me too much. I use Geist a lot and can use REX files in that, and I can also use Melodyne for time stretching.
The modulation feature is incredible and it's something I asked for in Sonar years ago as a sort of "pipe dream." There are other things that people have repeatedly asked for in Sonar as well, such as track folders in the console. I also love how you can have sub-folders within folders, and you can drill down into those folders in the arranger timeline so that it only shows those tracks in the arrangement window. Little things like that really help your workflow and make working with large, complicated projects much easier.
It's so much better than Sonar in a lot of ways. Like being able to implement things like multiband or mid/side processing on one track without having to route things to aux tracks. So if I want to apply distortion to a bass but leave everything below 250Hz untouched, I can just insert a device which splits the frequency, and each half has its own FX chain. Same thing with mid/side work. Again, these kind of things really enhance your workflow and help you manage the size and complexity of projects.
I also love how tracks are just tracks, you can freely mix audio and MIDI on them.
I bought into Bitwig not just because I think it's an incredible DAW now, which it is, but also because I think it has the potential to become an absolutely unmatched piece of kit in the future.