In thinking over the 10s are double successes idea, I've decided that a 10% chance per die of getting a bonus isn't good enough. There needs to be a more compelling reason for hewing to your ideals. Destiny dice need to be that much better when you're following the true calling of your heart instead of just being a big damn hero in general.
The double success idea is a good one. I like it. It's still simple and prevents dice overload. It just doesn't get triggered often enough.
So why not just take out the trigger and make it automatic? Act in accordance to your ideals, and any successes you roll on Destiny dice count as double, up to the rating of your ideals in play. Roll those dice over to 10 if it helps you keep track of them.
I think that's the version of the rules that's going to hit the next playtest session.