I'd love to have a setting on a per-ingredient basis that allows you to adjust how fermentable it is. At the very least, I would like to be able to mark something as 100% fermentable (for things like simple sugars, Candi Syrup, etc.). This would bypass the yeast's attenuation percentage calculation and would therefore have no impact on the calculated final gravity. A more advanced feature that I would like to see is a way to add a custom "fermentability factor" to fermentables that allows to adjust if an ingredient doesn't ferment out as fully as others. For example, I'd like to be able to mark certain Crystal malts or extracts with an attenuation factor of 90%, which would then multiply the yeast's attenuation percentage by 0.9 before calculating the FG. Something like lactose or maltodextrin could be set to an attenuation factor of 0% to indicate that it does not ferment at all.