This would give us the best of both worlds, enabling use to edit velocities and note lengths, overcome obstacles that one option can easily hurdle. Would also facilitate the learning of one option over another, and see the benefits of both.

 
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I like that idea. Hadn't thought of it previously, but that would be a nice feature.

As long as you can turn it off if you want. :)

If the piano roll view could display drum maps it would give you a possible articulation/expression too

Kamikaze
This would give us the best of both worlds, enabling use to edit velocities and note lengths, overcome obstacles that one option can easily hurdle. Would also facilitate the learning of one option over another, and see the benefits of both.

 
Some good advantages, but you haven't provided any description of how it would work. Presumably separate panes for SV and PRV would be inevitable because PRV has independent vertical and horizontal zoom whereas SV does not. Rightly so, since it is unacceptable to stretch a stave out of shape but perfectly acceptable for a note grid to be stretched or squashed almost limitlessly. And would the two panes each be vertically scrollable? The more I think about it, I tend to favour the existing system with 2 separate windows.

There is so much that could be experimented with.  This was buchla in the 70's?
I can see how a "hybrid" or "staff roll" could be really useful.  Or have the notes like Mixcraft where the notes can be "edited" piano roll style. 
 

 
 

A hybrid midi / staff (staff roll?  midistaff?  hybrid?) to allow editing of midi notes without "note heads" but with vertical spacing along a traditional "staff".   For those who are familiar with notation, this is a much better method, as you do not have to use the left side "piano" image and shaded lines to know where you are:  the note value is immediately known by its staff vertical position. 
 
Visual examples (crude) shown below.  There could possibly be a way to turn on/off the actual staff note heads, but this would allow easy editing in horizontal (time) on the raw data) but also tie it to the notes. 
 
I believe "Notion" has something along this line where the note duration in staff view can be optionally edited like a midi piano roll note, but I think this would be a first for any daw to allow very easy and slick way to combine midi editing with staff spacing.
 
 
 
 
 
Amiga "Bars and Pipes"

 
 
Mockup

 
 
Buchla Music (from 70s?  80s?)

 
 
 
 

Sonar is very good tool to record midi and clean up the notes in Piano Roll view so it will look good as notation. I can quantize and do some detail editing.  Today I can have both Piano Roll view and Score view open in separate windows and see instantly how my editing in piano roll view will affect the notation in the Score view. But it is not lined up on the screen. It would be nice if I could in Piano view select something like "Show/Hide Score Pane" in similar way as "show/hide controller Pane". So that the notation presentation is in the same window as the piano roll view.  And when I scroll or zoom the two will always be lined up.
 

Something that looks like this