Judges Guild had an interesting take on initiative which (as unmodified) roughly follows the same order as Holmes. It's much more complex, but it's all in one small table.
Holmes level spells (1-3) before missile weapons before melee weapons.
Using at least the first part would help resolve some issues that Holmes doesn't touch on (is a breath weapon a missile weapon?).
It's unclear to me whether "no armor" gains a +3 adjust or is included with light armor with a +2 adjust (below I assume the latter).
I like that it could allow for a highly dexterous archer to have a chance to disrupt the spell casting of a slower caster.
Missile Fire has a score of 9; Dex 17-18 & heavy armor = +3; total 12.
Spell of 1-3 level has a score of 10; Dex 9-12, light/no armor = +2 total; total 12. Totals are tied, so actual dexterity ratings are compared and thus missile fires first.
DF thread started by ken-do-dim in 2008)