Since i am jumping in with both feet (in development using stencyl), joints are something i have grievance with too..
There are a quite a few bugs in the existing joints system. The properties of a joint refuse to get saved sometimes. The scene window messes up if a joint is deleted. 'Should the objects collide' often doesn't make any difference..
and yea, support for the other box2d joints will be much appreciated in future updates, as you said elegently with dedicated blocks to them