Or what about this one right here that many, many people have been asking for, but has been languishing for years because it's not "interesting" to developers?
IMO, Thunderbird stopped being industry-leading or interesting from a UI/UX perspective years ago. As one who uses it on a daily basis, it makes me sad.
Things like Postbox show that the code base can still function well and can be used with some UI/UX love, but since Postbox is a closed project, the majority of extensions, etc. cannot be used with it unless they are "Postbox-specific" versions. (Note, I am not knocking them for this, just stating the facts.)
I just wish we had the Postbox UI with the community of Thunderbird around it...
Well, in my case I have an anaphylactic reaction to cats, including dander, fur, oils, etc, so having them in the closed-circulation cabin air could indeed be fatal.
It's especially worrisome since allergic reactions often intensify the more often they occur -- someone might not even realize that the next one could be fatal until it's 2 hours too late into a 5+ hour flight.