I was thinking that it would be helpful to some people to have a distance parameter for dynamic settings.
The idea of this parameter would be to track how far your brush has moved from the original spot you planted it. This would allow several things like force fade as well as size changes that would be less wavering like the speed parameter. This would also allow things like gradient made quick and easy (some people have been wanting this) as well as brush strokes that could resemble motion blur lines if paired with other settings.
Here is an idea of what it might look like.
I hope you consider my suggestion.