DDP does sound similar to pub/sub. Maybe it's derived from it? Another approach for sharing realtime data between multiple client/frontends is via operational transform or differential synchronization but that is very expensive and it appears difficult to scale beyond a certain point due to latency (good for collaborative editing of rich text documents, but I'm haven't heard of it being used in other contexts).

I wouldn't say operational transform is an alternative to pub/sub. The two could be used together.