I guess, some interop discussions and announcements can be relevant here (like if, say, MainTiddlyServer starts supporting TW5, too), but my previous attempts to talk about interop were not met with enthusiasm, so I’m not quite sure.
Perhaps occasional announcements, like new releases (Jeremy shared 2.10.1, likewise we can mention 2.10.2, too) won’t hurt, but neither they seem of huge interest here.
As for mixing all the discussions, I also think that it’s not reasonable to do so, just to avoid unnecessary increasing of congnitive load.
The only thing that I’m not quite sure about is a place to discuss meta-topics and ideas, where users of both TWC, TW5 and maybe some other platforms (like Obsidian or AnyType?) may benefit by bringing and discussing ideas together and sharing experiences. For instance, I think TW5 users may benefit from considering what was implemented in ExtensionsExplorerPlugin and everybody can benefit from discussing how to struct extensions indexing (taking into account more complicated cases, like multi-tiddler extensions, automated indexing of existing repos, proper handling of forks that are maintained more actively than the originals, etc). Another example: I know that the guys in Obsidian community are actively introducing AI into their plugins which may be useful for other platforms.