A meta-language approach is great for increased portability, but also requires a larger up-front effort than a single platform solution. You would need to need to define your meta-language, build the code generators and test. As you develop the application you will most likely need to evolve your meta-language toolset. Testing will also require that you test for each of the targeted environments. It's a significant increase in investment in order to capture incremental market share. I have no idea what Fog Creek's ROI is on their meta-language compared to the .Net only projects.