We will still leverage AIO and have no plans currently to remove AsynchronousSocketChannelStream. This is the default implementation that the driver uses for async.
Furthermore, there is not a hard dependency on Netty. It's opt-in (via a system property, though that may change), and if you don't opt-in, Netty does not need to be on the classpath.

But Netty gives us some advantages.

1. AsynchronousSocketChannel was introduced in Java 7, and we would like a solution for our Java 6 users. Netty is supported on Java 6 and up.
2. Our AsynchronousSocketChannel-based implementation does not support SSL, and adding that support is non-trivial. With Netty, it's just a few lines of code.
3. For applications that already use Netty for the rest of their I/O needs, a Netty-based driver for MongoDB may integrate better. For example, they could share an instance of an NioEventLoopGroup.