The new WildFly 11 adapter is able to start the server, but when you stop it, you get an error:
Server WildFly 11 failed to stop.

Rob suggested to set up credentials and then it will work. That's true, but it still doesn't explain why this doesn't work without credentials locally as it should and as is the case with all the other server types.

To make sure this works outside of Eclipse, I started WildFly 11 from console, then in another window I ran jboss-cli.sh, connected (no password) and then was able to shutdown the server successfully.

So this needs to some investigation as to why this fails from Eclipse.