I'm looking over your stuff and I like where your ideas are headed. You cover a lot of topics in your write up on Github. My thinking has been towards a much smaller feature set, specifically one that would help the most busy people who need the product most. After this has been achieved with a solid market share of the target market, then we begin adding additional features.
One of the major hurtles, is that email is intrinsically different for everyone. A great email solution is one accepts this natural hurtle and uses it to create an economic moat against the inevitable competition.
While I am not an expert in email or programming for email software, I have developed a feature set and interface that I believe would solve these email issues.
This project is important to me, because I think it would not only improve my life and productivity, but the lives of many others who are enslaved by emails.
There is no contact info in your profile... I'm interested in the email idea, check out https://github.com/alain94040/coolbox for my own list of ideas regarding email.