I don’t like this at all as a Delta Chat user and I urge the devs not to fragment the app in this way.
I want to write emails like chat to MUA users and have it be totally transparent on their side. I like that my subjects are formatted as the first few words of my email. It frees me from thinking about what it should say and provides good, glanceable context.
I want replies that are threaded and no Chat: prefix added. It is ugly and confusing to MUA users. I want all of this in a client that does not try and separate MUA users from Delta Chat users. It is a bridge between the worlds I appreciate and I hope the opinions of a few people loudly protesting do not drown out us other users.