Is there a reason why postgresql schemas (available since 7.3, although it's possible they were not fully functional until later) are not used? It seems like they would be a little nicer to work with than the '__' namespacing convention currently used, although such a change would be mostly cosmetic. Such a change would be huge, but maybe individual packages could adopt it.

Another mostly cosmetic change that would be nice to adopt is the availability of anonymous code blocks, (i.e., 'DO ...' rather than creating a function and calling it immediately), but that's only since pg9.0 which is at least for now too much dropping backward compatibility.