The moderators on communities that have decided to approach this in this way will discuss it amongst themselves and begin a thread requesting a new feature on the github. In the meantime, the moderators can work together to sketch out a plan of how to connect their communities in a loosely organized manner, where each community links to one another, and cross-posts will be recognized, while not explicitly favoring one community over another. Basically, just moderators working with other moderators and communicating and making a plan that works for those communities, and will likely be different for each set of communities.
If the feature fails to gain traction because there aren’t enough interested parties, then oh well. Maybe one of the interested parties knows a little Rust and will write in the feature themselves and ask for their work to be added to the mainline project. Anyway, these things take time, and running around howling about how it won’t work before people have even really had formative discussions about it isn’t helpful. Yeah, it’s decentralized, which means some people will take longer to find out that the option exists, because they’re on a site that isn’t federated with somesuch other site, and the meandering path of news of “tools to organize multiple communities as a larger whole,” might take longer to get to them. That’s… not the end of the world, you know? That’s the nature of decentralization, initially, the conversation won’t involve everybody. Over time, maybe it will, but likely some areas of the fediverse will wall themselves off and not be interested in connecting their communities to others and that’s fine. That’s literally the point of the federated decentralization, so people can be allowed to make their own decisions on how to interact, everything from not interacting at all, up to and including making “webrings” of related Lemmy communities. I’m not sure why you need a whole gameplan laid out for you, but it feels like maybe you haven’t been part of a lot of self-organizing communities in your life. These things grow organically. Yes, that includes competing standards growing at the same time, much like there being a bunch of different Lemmy apps existing at the same time.