You actually can't override a few of the events such as Control-W [1], however that could easily be fixed by using an alternate keybind for the game instead.
This port uses a proxy for networking, as the main game uses UDP-based networking [2]. Perhaps it would be possible to upstream basic WebSocket/WebRTC packet-wrapping support to the servers in the main Minetest project?
WebRTC data channels would be ideal, so that clients can connect directly to servers (or at least regional proxies) in a UDP-like way. Vanilla minetest would need to include an WebRTC endpoint for this to become universally available. There are lots of details that would need to be worked out.
I definitely did overwrite it in my app, but I just checked and remembered, that you also have to be in full screen mode.