the one thing that comes to mind is Java. Now that OSX runs a current JVM (1.3.x) you would be able to run a very robust Java object model, including i would imagine a full J2EE system which would allow you to do full EJB remote object (EJB = COM+/MTS, straight Javabeans = COM)
heck, right now i've got apache jakarta Tomcat running to do javabeans! which totally rocks btw...
Yeah, but it would be nice to have something as easy to implement as ActiveX communication.
Sure we'd prefer it not be some proprietary nonsense, since there <em>are</em> legitimate open standards for such things, but seriously, have you ever tried to set up your own JavaSpaces? J2EE server? It would be so much nicer if there was a system-supported communication standard (which there may be--I don't know).
Even nicer would be if some of these standards like CORBA could be the "native" language for OS X high-level communication.