Multicast may well be shitcanned to an expensive slow path, given that multicast is rarely used for high bandwidth scenarios, especially when multiple processes need to receive the same packet.

The main real use of multicast I’ve seen is pretty high packet rate. High frequency traders get multicast feeds of tick data from the exchange.

multicast is precisely used for low-latency high-throughput message buses.

With multiple processes listening for the data? I think that's a market niche. In terms of billions of devices, multicast is mostly used for zero-config service discovery. I am not saying there isn't a market for high-bandwidth multicast, I am stating that for the vast majority of software deployments, multi-cast performance is not an issue. For whatever deployments it is an issue, they can specialize. And, as in the sibling comment mentions, people who need breakneck speeds have already proven that they can create a market for themselves.

That's not a market niche, that's the normal mode of operation of a message bus.

The cloud doesn't implement multicast, but that doesn't mean it doesn't get used by people that build non-Internet networks and applications.

I will reiterate that most if not all desktop/laptop class x86 hardware as it is deployed in the wild does not care about multicast performance.

Those are Internet devices.