As may have become apparent, I really do love the multiplicity of die-types used in D&D, and I like to use them all wherever possible. Rolling for initiative in combat seems like an ideal candidate for expanding the dice pool in a way similar to my idea for the surprise roll, and the type of die rolled for initiative would depend on the character's (or monster's — we'll get to that) DEX score.
|DEX Score||Initiative Die|
|20 or more||d20|
|3 or less||d2|
There are pros and cons for this system.
Con: It would require individual, rather than group initiative, which can slow things down a bit at the table, and in a large fight it can be easy for somebody to miss their turn, evoking howls of outrage and demands to rewind the action so that they don't have to bear the penalty of their own egregious lack of attention. However, we used individual initiative quite successfully in our D&D3e days, using my Patent DeLuxe Initiative Board and little slips of card with the character's name written on it.
A similar board could be used for this system, but it would be smaller, only having to go up to 20 (unless one included a d30). It allows for characters (and monsters) with multiple attack routines to see just when they come in — I'd suggest 5 spaces down the chart from their initial initiative placing, with a minimum of 1.
Con: It would require that all monsters would need DEX scores. That could mean a bit of work for the GM rolling them individually, or else it could mean that he or she just use the DEX scores listed in the 3e monster descriptions in all the vast number of 3e monster books he or she already owns and are just sitting there on the shelf doing nothing.
Pro: It opens out the initiative system to accommodate quick, high-DEX characters without making them invariably the first to get an attack routine. Even if you're throwing a d20 and your opponent a d3, there's always the chance that you might throw a 1. I like that, because when it happens the groans feed the darkness in my bitter, twisted heart.
Pro: It gives the players the illusion that they have some sort of individual control over events. It's so touching that they think that.
Pro: It uses all the funny shaped dice. What's not to like about that?