FWIW, I never considered that a serious limitation. On my phone, I don’t want to read email. It’s a sub-par experience, especially if you’re used to Sup/Gmail/Notmuch. You can’t just go back to “regular” email clients anymore :).
As for using multiple computers: with sup I used to run it in screen and attach that screen session whenever I needed it. With notmuch, I can just tell it to run notmuch(1) on a remote machine and even use a local UI.