Scaling of PubSub for a FB like notifications app


I’m planning to use for an app where users connect to a notification stream (Topic) and listen for notifications(Publications) from the server(Publisher).
If there are thousands of users, then there will be Thousands of Topics.

My biggest concern is, can I scale out Crossbar to several nodes and spread the connections across nodes for horizontal scaling? I’m only using PubSub part of Crossbar, no RPC, etc. All the web clients will be subscribers only and a web service will be pushing publications to the Crossbar.

And also, How is this having thousands of topics effects the system? When planning for scaling, I should worry about spreading the connections only or I should worry about spreading the topics also?