In order to be concrete about the sorts of things we might work on if we had a literate programming system as part of PlanetMath, check out http://mathulator.com and http://calc101.com. These are for-pay services that you can use to get answers to various math questions.
There is no reason why we couldn't also provide for-pay services using the same model, but with a free software backend.
People who contend that PM shouldn't restrict access to site services might object to this, but we could argue that since the software is free, its use isn't really restricted.
The hurdle of actually being able to compile and install the software may be too much for some people. Or, some computer-savy person might make a stand-alone program using the code, and provide that. But PM would still be in a good position to "advertise" its own service, since it is already a popular site.
As the HDM tools develop, we should be able to provide increasingly sophisticated question-answering services.