For me, the default makes sense, too, in the very specialised cases (in the world of things that have types) like settings of a web server or cvs parser, where the application author defined it for to quickly launch some program or function. The 'default' there would mean 'something sensible', the meaning of which I don't yet care about. Probably the author of the package is also a frequent user of the default to test the thing he is writing.
So I would be +1 for adding a class to the base (as many would otherwise re-implement it anyway), but with no instances. The module could also state the policy behind the class, i.e "don't write defaults for widely used types/types that you didn't create yourself" or whatever else people agree upon.