I support you on replacing email. But it should be well integrated to the concept of emails, as
1) I don't want to use another system over my system (only if it replaces my all email system)
2) I need to be able to use opp.io also if not everybody uses it (It's taught to make other to use a new system)
3) Most of my tasks are something to do with emails (as in your example: write an email to the costume)
We're taking a slightly different approach with our startup, MorphMail (still replacing email, but not going the todo list route): https://www.morphmail.com/
I really like the opp.io way of messaging. We are very excited about the idea, even if it needs some fixes, but hey! it's still not in beta yet!
We look forward to use it every day basis in our team.
Definitely looking forward to the beta, will try it.
Are you thinking about integrations with task/project management systems?
Yes, definitely. We want to integrate to both "directions", both to communication tools - with things like a gmail plugin - and to pm tools.