It’s useful that the rhythmic grid has relative durations. Could that also be available for selecting rhythmic durations? (e.g., I’m on quarter note and I can press a key command to go to the next doubling or halving of duration)
This would reduce the number of keys needed for duration commands when working on a laptop while still making it relatively easy to get to needed durations.
Out of curiosity, can you explain more thoroughly how what your process would be? Genuine curiosity here because it strikes me as just as easy to select 1-9 at the top of the keyboard as it would be to press a dedicated +/- key command.
If I may jump in…
It would be beneficial to not have to move around and select the correct number if there were a dedicated “+” / “-” increment/decrement function. (No hunt and peek). I am a good typist, but the number keys for me are a tad too far away from the letter keys to feel comfortable in terms of memorizing their locations. (I am getting better, though). On another point, I would LOVE to see Dorico put on the screen the current duration in some form when the durations panel is hidden. I would bet just about every Dorico user has had or continues to have the experience of trying to remember the current note duration, or simply affirmation that they have the correct duration for the next input! Perhaps even a subtle semi-transparent fairly large note icon that fades away subliminally… Just some thoughts… 
I would certainly love to see the input karat show the duration with the little note preview. No doubt “the team” has thought of that. I’d guess it’s already on their list.
I love my MMO Gaming Mouse (10 year old Razer Naga) that’s bristling with programmable buttons…and I don’t even play games 
Even with a laptop, it’s worth it to me to pack a really nice mouse with a ‘ton-o-buttons’ all over it.
Just an idea.
Also, there are probably options out there to turn your smart-phone or tablet into a kind of wireless tag along 10key pad (or any other layout you’d like)…since you’re likely to have that with you on the road anyway.