Java and .Net Link

I find this project interesting but I question whether you would ever want to use it in a real production implementation. I'm trying to come up with a case where you would hook in down at this level from Java to .Net instead of at a higher service level. Why would you mix the two? If you have chosen Java over .Net I'm assuming maybe you are a Java shop. You might like the portability of Java. If you need stuff from Windows that only .Net can provide then why not just write it in .Net because it's not going to be portable at that point any way. This Java-.Net link seems complex and brittle to me. Cool but practical?