I'm a bit surprised by this statement. Does this imply that there are now a bunch of FOSS projects that don't use mailing lists? Mailing lists are by far my preferred method of communicating with projects. Please don't tell me people are moving to github issues or some such?
FOSS projects should communicate over open protocols with a variety of interoperable implementations -- whether with tried and true tools like NNTP, mailing lists, and IRC, or more novel solutions like Matrix -- instead of allowing a proprietary third-party web application to present a one-size-fits-all interface and function as a single point of failure for project coordination.
You can shake your fist against the tide as much as you want, but a lot of projects are populated entirely from people who grew up after the web was born, and their members see no need to keep looking back to a system designed for a world before TCP/IP itself.
"Message organization" is one of the most significant elements of this particular use case. Maintaining well-organized archives is extremely important, and it's not enough for messages merely to be searchable -- they should be easily browseable by topic and time range.
Discord is out not because it's proprietary, but because it doesn't have usable history. They could be GPL and they'd still be bad.
Discord's lack of searchability is certainly a biggie, but having all history locked away and unexportable in any way is the worst part of it.
And damn the two similar names are confusing, I find myself typing one when I meant the other...
Another annoyance are projects that choose to autolock threads in Discourse. On a technical forum such actions are unwarranted as there are times when an investigation can take months and remembering to add a nonsense post to keep a thread from autolocking doesn't always happen. So, a collection of disjoined threads result and even with links to the prior thread(s) the flow of investigation is greatly disrupted. SMH
The fact that there is little real progress can be suppressed.