Wow, today's my day for posting :-)
Some thoughts on MetaData (for DataModel columns):
Small improvement, but what about adding a default label of "valueX" where x is an incrementing number (static to the class)? This is just a little nicety if, for instance, a bunch of data is read into a DataModel with no label information
There is a @todo on SetLabel. Is this still to be done?
How do you envision maxValueCount being used? It seems to me like simply changing the column class to collection.class or List.class would achieve the same thing while being a bit more straightforward.