Rewriting ancient code

Quite the contrary, open source geeks focus too much on tech debt and too little on making sensible UI/UX choices. In fact, your own comparison with GNOME is evidence of this: GNOME is one of the most corporate (and thus client focused, because that's what makes money) led DEs we have. It's often called a Red Hat project, even. Compare that to everything community led and see how often those change. The only real example I can think of is when KDE switched to Plasma. Otherwise, everything looks and feel more or less the same than it felt 15 years ago. Even with Wayland, most compositors are more or less clones of some existing X11 window manager rather than something completely new. Open source geeks surely like their UIs to stay the same over time.
Regarding users who internalized the quirks, maybe some projects are interested in actually attracting _new_ users that have higher standards than adapting themselves to software. Software is meant to serve the user, not the other way around. Only geeks and people with very specific needs (e.g. privacy conscious not trusting the proprietary alternatives with better UX) are interested in sacrificing usability to serve the whims of a decrepit email client.
Firefox didn't lose the browser wars because it changed UI, it lost way before that. It lost the browser wars because of several other factors, one of them being too static to catch up with the competition. The change was probably good except for power users, but it came too late.

> For sure, the current UI is inconsistent as hell. The Calendar component is way less functional (and more ugly) than what Google manages to do in pure JS. The AddressBook looses out big time when compared to managing the data in a huge spreadsheet. The chat... I have no idea - I never used it ;-)
> But email management? I think that was nailed years ago. And that's what every current user is most likely afraid of - seeing the cherished mail-management experience be dumbed down to the levels of, say, Gmail or android clients.

You say this as if dumbing down is really that bad. Those clients are, apparently, _very_ _practical_. Thunderbird was always meant to be for the general user. If it allows for configuration, extensions, or whatever mods for power users to suit their needs better, then great. If it doesn't, then find something aimed for power users. But if you aim for general public, your defaults should be what a regular user would expect. And most users don't cherish their mail management experience, they mostly see it as a tool that needs to get out of the way as soon as its work is done.

> And, monthly releases: how can someone think it is a good idea, for a mature product? The only reason I can think of that being necessary is if A) there's a constant stream of security issues being found, or B) the devs expect to be trashing around a lot the UI and functionality. Is that what users really want?

People don't like waiting 6 months for a trivial but annoying bug to be fixed.

> Back on the topic of the video: for all the declarations that it contains, of love for the community and for the product, it reminds me strongly of similar situations I lived through with other OSS projects, when new UI experts and Product Managers were brought onboard who, for all their good will, were clearly less competent than the unruly/incoherent/unvisionary bunch who preceded them, but were too stubborn and proud to acknowledge it, and tanked the product hard.
> I guess many people around here will have got similar "gnome devs" vibes...

Unvisionary is probably good, visionary is risky and it could end well or it could end miserably. Visionary can also be reverted if failed, tho, while unvisionary will always remain static.
The other qualities tend to do poor UX. I dislike PMs just as much as the next programmer, but UI experts exist for a reason. Programmers tend to write code for other programmers in the best case, and for the code itself in the worst case. That doesn't lead to something most people will want to use. Just look at most TUI MUAs and how many users (even among geeks) they have compared to Thunderbird or webmails or Outlook. Sane defaults and a little bit of usability could make it at least an order of magnitude more popular than they are today, but leets gonna leet.

Indeed, and when the product finally works as it should after a decade of work, the entire thingie is seen as technical debt :-)