I haven't had the time to try this. But my issue with built-in AWS forecast is it'll be totally inaccurate once Reserved Instance come into play.
Does CloudForecast solve this issue?
We treat Reserved Instance spending differently in order to provide an accurate forecast. The spend will be treated differently based on your purchase type (All Upfront, Partial Upfront, and No Upfront). Please reach out at francois@cloudforecast.io if you more questions.