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The official websocket plugin is just concerned with sending messages between clients (like a chat feature). The good thing about this plugin is the ability to communicate objects of data (JSON) with clients and servers which is what you need for multiplayer gaming.
These plugins will come on a lot over the next year or so as UDP becomes accepted in browsers.
Yes, you are correct about the prediction. It's called Client Side Prediction and can vary depending on your game.
Concepts such as CSP, Lag compensation and inter/extra-polation are difficult to grasp and because they integrate with the game mechanics, you don't often see 'plugins' for such things.
Also, because of cheating, you need to simulate the game on the server so can't really get away from learning how to code. This could in theory be implemented into Construct but it would require major effort and good design thought from the developers.