There is no requirement to use polling or sockets. If it isn't relevant to your users or server side then don't do it.
But the bar now is that users expect their displays to automatically update promptly, and they don't care how hard it is for you to implement. You don't have to do the level of complexity you think. For example there is no need to tell the client there is an update, or the details of the update. All it needs to know is that there could be an update. It can then go off on the regular HTTP connections to see what is new/relevant and that will go via your existing servers/caches/load balancers etc.
But the bar now is that users expect their displays to automatically update promptly, and they don't care how hard it is for you to implement. You don't have to do the level of complexity you think. For example there is no need to tell the client there is an update, or the details of the update. All it needs to know is that there could be an update. It can then go off on the regular HTTP connections to see what is new/relevant and that will go via your existing servers/caches/load balancers etc.