They use screens and color cues for performances where a live orchestra plays back the soundtrack of a film in sync with the projection. Professional musicians are a lot more open to alternative representations and technology integration then you might be aware.
The screens are for the conductor, not the musicians. They're following the conductor's direction and don't need to know what cues they're playing to, nor can they take their eyes off their score.
There simply isn't the money in the budget to bugger about with clever ideas in a sync session. Merely having a session with an orchestra is already a luxury for many productions, because most composers can knock out a reasonably convincing orchestral soundtrack in VSL at a fraction of the cost.
An orchestra is an extraordinarily efficient musical machine if they're doing what they were trained to do. If you want innovation, don't hire an orchestra - experiments get very expensive very quickly when you're paying ~$50 a minute for the privilege.
No, the height increase is only by a factor of 12/7, which is about an extra 71%. Compensating for this, there is a width reduction caused by the loss of accidentals. There is also no need to waste space on unused octaves, so there might not be any height increase at all for some pieces of music.
Trivial transposition is a highly desirable property.
Starts to sound a lot like the same kind of thinking that gave us service oriented architecture and a new javascript framework every week. Just hire shitloads of more people to make sure it all works when it needs to. Because it's easier for beginners! In fact, with this new notation system that simplifies everything so much, you could probably fire all the older more expensive musicians in the orchestra and hire a bunch of juniors for a lot less money!