Yes. I think several clients have open feature requests. The Stalwart documentation has a list of projects. There is one command line client as of now. But I'm not switching to a cli mail client or proprietary software, so I've postponed it. We'll see where this is going.
I welcome these modernization attempts. Though in theory I'd love to see someone revamp email in its entirety, add encryption, signatures, chat and crack down on spam and phishing. Not sure if that's ever going to happen, but that'd be great, too.