Lego NXT support

NXT doesn't run on java... What you are saying is they would have to make their own compiler. Kindof like rewriting java.

You can use eg LeJOS to allow programming NXT bricks with Java but I don't see the point of Greenfoot integration. To be honest I'm not really sure what you're asking for.

Why? Greenfoot's a special-purpose IDE; why not use another environment that's more suited? There's no screen on the NXT brick so you can't display the world or the actors. Most of the Greenfoot concepts are just irrelevant. If you like the editor and general simplicity, perhaps try BlueJ. A web search for "program lego mindstorms with bluej" shows some results that look interesting.

It looks like you can use the LeJOS NXJ API to read the sensor values. Just use the library as you would any other library (search the web for how to use the LeJOS libraries with BlueJ and/or Greenfoot, I'm sure there will be something out there). This doesn't require any special support be added to Greenfoot (unless I'm still not understanding you).

There is a support library (and documentation) for using Greenfoot together with Finch robots, but they aren't integrated in any real sense. If all you want to do is read sensor values, I think you can just use a library as I suggested in the previous comment. When you said: I assumed you meant that you want to write code in Greenfoot which would run on the brick. You certainly can't do that with the finch!