Email is more than a technology its a community. There have been plenty of technical attempts at replacing it but they have failed to un-seat email because they focus only on the technology aspect which as you have found is largely a solved problem although... getting the details right might be hard. You need buy in from the community which is not just users but also businesses and organizations that use email which is everyone from CEOs to church leaders. It's not enough to fix email you have to get buy in from the community to make a meaningful change and I don't see anything here that would do that. This isn't really a criticism, just an insight I offer. I work in this field and we're trying to get out of it cause managing email sucks. I would love something new to take its place but the community has heard so many promises that never came to fruition, when that happens you either need a better promise(harder than it seems) or you need credibility which may be very difficult in the current climate. Not an unsolvable problem, those don't exist but sometimes the lever you need to solve the problem is further than you can reach alone and this is one of those times.