Personally, I think Netty brings more pain than benefit to the project. It was a good starting point for the project because it had WebSocket decoders. But Aslak has reimplemented these anyway, and the cost of keeping up with Netty has been high, and I've found it more of a hindrance at times.
Last year I also spiked out using a JNI wrapped libuv based implementation. The majority of the code was written in C, with some high level Java bindings. It was much faster than the Netty backed implementation, used a single thread and was much better with memory and GC. It looked promising, but I decided to abort because adding C and JNI to the project brings in a lot of baggage both for the dev team maintaining the code on cross platforms, and for the Webbit users.
My choice would be to use java.nio sockets. It's not pretty, but you know exactly what's going on, it's pretty close to the operating system networking stack, it avoids any extra dependencies, and a lot more stable.
The only downside I can see for losing Netty is that Webbit would probably have to drop SSL support (it's a real pain trying to manage SSLEngine through a state machine - the Netty abstractions made it pretty easy). I'm ok with dropping that functionality, as I recommend using an HTTPS frontend offloader anyway (e.g. nginx, haproxy, stud, pound, stunnel, etc...).