The Chronicle of Higher Education has an article about standards for courseware and CMS allowing “mix and match” development:
For the first time, evolving technical standards for software are making it possible for colleges to customize distance-learning programs by easily mixing online-learning software from multiple companies.
This is of course exactly the approach to a CMS system that makes the most sense to me. One of the standards the article refers to is SCORM, “the Sharable Content Object Reference Mode.” Here’s a good overview of SCORM. The difficulty is that talking about a standard is one thing; actually adhering to it is another, far more important step.