The idea
Neo currently uses a variant of the Apache Torque schema format to describe the domain model and usually developers edit the XML file in a text editor. It has been suggested to look at ''real'' modelling tools and use Model Driven Architecture (MDA) technology to transfer the model to Neo. In practice this would mean to implement a new model reader that can read the XMI format.
Resources
Below is a list of some Open Source tools and frameworks for handling UML models that might provide an inspiration for the development of the XMI reader. Unfortunately, none of them is .NET based.
AXgen http://axgen.sourceforge.net
This is a Java tool that reads XMI, builds up its own meta-model and then uses Velocity to generate code from this meta-model. This is pretty much what we'd want the Neo code generator to do; except it has its own meta-model in the Tools.Model namespace.
XCoder http://sourceforge.net/projects/xcoder
Another Java framework that allows model transformations with XMI input. This is in active development and one of the contributors is an old friend of mine (Erik) which might help.
NSUML http://nsuml.sourceforge.net
A complete UML metadata framework which, of course, supports XMI. Like the other ones it is implemented in Java.