I haven’t tried to do it, no. It’s out of scope for the intended purpose.
But also, the proposed API probably would prevent web apps from succeeding at the suggested kind of peer-to-peer multicast in practice, even if it’s possible to get the browser to emit multicast packets.
In order for the packets to be received by this API at a remote peer, they’d also need to receive an authenticated AMBI stream, advertised via a DORMS server with CBACC info that provides rate limits.
(If the source is inside a NAT that the receivers are outside, it would probably get more tricky still, but I think those barriers would already be pretty severe for most web apps.)
I’d be interested to see a script that did send multicast packets from a browser, but I don’t think that would be sufficient to enable the usage I think you were asking about.
To be clear: I’m not completely sure it’s impossible to make this work with sufficient effort from the sender, but the API is very much not designed for that use case, and I expect that even if it’s possible, it would be much easier for the sender to operate a service that accepts messages from the sender and transmits them to subscribed receivers from that service.
If I understand the use case you’re asking about, it might be possible that future extensions might help it, but I doubt this API can do it directly from one browser to a bunch of others. (However, it could help with making an external server that could relay messages to many others.)
I hope that helps to clarify.