The only reason DAWs are so deep is because they have to be all things to all people. I've never used half the features in Cubase and I do everything from track live country bands to death metal to trance MIDI productions and even made a few attempts at movie scoring.
Personally, I don't find Cubase remotely complex. I find MUSIC complex, but at this stage I don't see Cubase to even remotely be a hindrance. Is there a learning curve? Definitely. I just accept learning curves as a part of life and don't find issues like "where is this button or feature?" to be as complex as understanding black holes. It's REALLY easy stuff you have to do a bunch of times. So I think it's an issue of time and/or laziness more than difficulty.
As for busting it up into different phases, I'm listening. What exactly are you going to bust from what Cubase is already doing?
I'm all for revolutionary ideas, but I'm going to need more information on what you are wanting to do, exactly.
I'd take Cubase and add formant pitch shifting, VCAs, automatic key detection, and whatever else I've talked about this week.2) If you could build your own DAW, what features would it have?
I'd prefer to avoid the keyboard, mouse, control surface, and console and have a direct brain connection. That would be faster. (Don't laugh, the technology is out for video games now.)