on the contrary for the first point. i suspect that most enjoy notmuch with their traditional interface because there are not many alternatives. probably most people looking for interface alternatives switched to gmail.
commandline UI development in particular seems very conservative, and attempts to explore new interfaces are rare. that's why i love this topic and am getting excited about any attempt to change that.
i obviously can't comment on what it takes to integrate notmuch with lumail, and i grant that one may possibly have to develop a mailclient with notmuch in mind for it to work well.
http://www.mutt.org/ Mutt for email of course.
https://vifm.info/ Vifm file manager, I am using it for everything, not having any other file manager on my system.
https://github.com/pimutils/khal Khal for calendar.
https://github.com/scheibler/khard/ Khard for contacts.
https://github.com/pimutils/vdirsyncer Vdirsyncer to sync calendar and contacts with any web calendar service.