One of my goals for the final version of Great & Small is simplified rules using a unified dice resolution mechanic. Which is the reason I settled on the current engine, 2d10 +/- modifiers = 20+ meaning a success.
My current version of initiative has always felt too clunky to me, though. I adapted it more or less as-is from B/X and the Rules Cyclopedia, but I've never felt it works simply enough for my design goals.
So, here's a streamlined version, that will likely replace the version in the Quick Start Core Rules. The change alters the niche ability of Runners, as well.
Your initiative equals your Total Level (or Hit Dice) + the Speed of the action you are declaring. Higher total scores go first, then next lowest scores in descending order. In the event of a tie between player and BM, both sides should roll the core dice and add their Total Level (or Hit Dice). The higher result wins.
Changes to the Runner niche
Under these revised initiative rules, Runners now add their niche die roll result to their total initiative score, instead of having all actions default to a Speed of Quick. Thus, Runner characters' initiative equals Total Level (or Hit Dice) + Speed of declared action + niche die result.