Hi Dima,
there exists a limitation for the number of AMC channels bound to WebSocket connections which can be adjusted using profile parameter, but for pushing messages to UI (WebSocket client) there exists (more or less) no limits for the number of messages transferred to the WebSocket client. Our tests, partly based on loadrunner, show that it is very hard to reach those (theoretical) limits. Just try to simulate the "heavy load" situation in your development system and if you would see any issues ,e.g. dropping of message just let us know.
We have a large number of unit tests which checks the consistency of ABAP Channel infrastructure. You as developer has also to test your software as good as possible, from different perspective, also regarding load test. Actually by increasing the number of AMC/APC producer you are able to generate more messages per seconds on the connection but you have to ensure that the consumer(s), e.g. the browser, is able to handler/consume those messages as well. My observation was, that if you send more than 100 messages per miliseconds to browsers you may observe issues regarding handling of those messages. Of course this depends on the JavaScript code and underlying library and garbage collector.
Cheers,
Masoud