I would like to stick to Java first. Because this project is eventually an open source project. And java is still one of the mainstream programming language nowadays although groovy is based on java as well. However, I feel it will encourage more folks to contribute faster without learning groovy in advance.
I agree with you here, scripting can be quite powerful but I think especially considering we want to build a framework, Java will provide the easiest way to make a pluggable architecture.
Assuming no one else objects, I think we should press ahead using Java!
Definitely want to stick to Java.