That's a really tough question.
The author of Workman doesn't like lateral movement:
http://www.workmanlayout.com/blog/
And some people hate using their pinkies, and have other personal preferences/annoyances.
I'd never used my pinkies for typing before using Dvorak, it was quite hard to get used to for me. Feeling quite awkward at first. Now I actually enjoy the movement of little finger and index finger to forefinger but not so much ring finger to forefinger. Which highlights the complexity and nuances of certain permutations of fingering.
Inward rolls (as above) are favoured over outward rolls.
I mentioned the clarinet, because if I were starting a layout afresh, I'd consider an ergonomic alternative to using the conventional standard keyboard.
I'd try and find some information about finger agility/dexterity with reference to playing music: piano / guitar / wind instruments.
Some stabs at early typewriters started with something that resembled a musical keyboard and evolved from there.
Going full circle:
http://www.sciencedaily.com/releases/20 … 085432.htm
Some typewriter curiousities:
http://io9.com/the-curious-evolution-of … -509985235
Do post your findings.
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Physicians deafen our ears with the Honorificabilitudinitatibus of their heavenly Panacaea, their sovereign Guiacum.