I have not worked on reimplementing the groovy templates feature because Java templates work in Groovy editor. I probably should have removed the preference page from the eclipse preferences, but I did not.
I recommend that you try creating a Java template and try it out in a groovy editor. It seems like most of the functionality would transfer, but I have not tested this in depth.
Can you try this and comment here on what is missing (if anything) from creating and using Java templates in Groovy?
One thing that I know I need to look into is adding a new template context specifically for groovy, but that could come later.