It's not that simple, it needs realtime communication between  both users, the only way is socket server. I'm using a VPS for this free server, there is no negative impact on sites performance because your server doesn't load extra data from anywhere. In case that the socket server overloads for some reason, the users won't notice it and the typing indicator will not be displayed in that period of time. This server can handle millions of users connected at the same time.

I will release the socket server so you can install it on your own, it requires basic knowledge on nodejs and you need a VPS or nodejs server. You need Knowledge on reverse proxy so you can make the connection between your users if you have SSL (https) in your website.
If you try to implement the "Jquery only solution" 2 things will happen:1- Your server will overload because you need to ping your server every 1 second (or less) from all users and your hosting company may think that you are under DDoS attack.2- Realtime communication will not really work.

Senior Developer.

Gotta say your pretty goot at this stuff. You've mentioned you will fix this on the next update I'm afraid I got no choice but to wait. Just not feeling good about being dependened on third party service. 

There is nothing to fix, because there is nothing broken neither bugs. What I will do is release the sockets server code so you can install it in your VPS, Dedicated server or Nodejs server and point this plugin to your own socket server instead of using my free socket server.

Thank you.

Senior Developer.

Thanks