The main issue with the sugar based powders is the very hard-to-control carmelization process, which gives uneven velocities, and in the case of "American Pioneer"-- has resulted in folks pouring water out of their barrels (literally) in high humidity enviornments.
The American Pioneer re-release does not seem to have addressed those issues. Triple 7 is far more consistent by comparison.
When it comes to sulfurless BP subs, there really isn't much that can be burned other than sugar. The carbon has to come from somewhere, if we aren't burning charcoal than it has either been fructose or ascorbic acid based products. It looks like someone will have to go a long, long way to top Triple 7 at the moment.