Some people love saying Mastodon/OStatus is very scalable because of federation but let's be honest that's some bullshit. It's easy to split and multiply, but that's not scaling.
The birdsite is much easier to scale.
@CobaltVelvet What you're talking about basically is a multicasting problem. That's got a long history in networking, though how that would work in m6n might be up for consideration. With a dedicated server, the idea of /local/ subscriptions to that server, handling the multiplexing on the local instance, might make more sense. The brand would lose access to the specific distrubtion list, but would gain audience. An interesting trade-off.