if you want to forward your module/block invocation to a template engine you can do it. nothing prevent you from doing that :
for instance, you can have a template service let's say VelocityService if you like it and use it from your module to render the content.
We are supposed to add support for jsp as module/block but don't have enough time to do it.
files would be database stored and compiled into classes. then a module invocation could be mapped to a class method that would be executed.