Thanks for mentioning Screenful. Just wanted to comment on your remark:
"In general I'd like to be able to just point a tool at N "completed" GitHub projects, and a fresh one - and get a forecast that adjusts as issues are completed and added (possibly filtering on issue tags in completed and new project)"
That's exactly how our Forecasting chart works. You can import any number of repositories and projects (classic or new) and get a forecast for the remaining work. You can learn more about that chart from this guide: https://screenful.com/how-to/how-to-read-the-forecasting-cha...
I like the fact that you're trying to unify the whole app dev lifecycle. But what about requirements management, don't you consider that as an essential part? Also 99% uptime is not really a 'rock solid' I hope you can improve that along the way.
"In general I'd like to be able to just point a tool at N "completed" GitHub projects, and a fresh one - and get a forecast that adjusts as issues are completed and added (possibly filtering on issue tags in completed and new project)"
That's exactly how our Forecasting chart works. You can import any number of repositories and projects (classic or new) and get a forecast for the remaining work. You can learn more about that chart from this guide: https://screenful.com/how-to/how-to-read-the-forecasting-cha...