I like the ideas so far. The ability to pass around message objects and Java beans is pretty neat, but then again any time you are doing something weird with functions (like pushing them around a network encapsulated in an object) you have my attention.

I have a doubt about the NACK approach. Most game implementations that I've seen have the following networking characteristics:

* Clients send user input events to the server (Synchronized)
* Servers send game events to the client (Synchronized?)
* game events >> input events

Under those conditions user input could be lost for a long time if it is infrequent enough. This is even more likely if you're doing game events as a UDP stream on the assumption that a small number of dropped packets won't be noticed in future updates.

Anyways, you have my interest. Looking forward to seeing more in the future.