You can already describe URI parameters in structured way with the new API Blueprint format. Refer to https://github.com/apiaryio/api-blueprint/blob/master/examples/7.%20Parameters.md for details.
The new format is now default and URI parameters are properly rendered in the documentation.
We are still working on description of http message–body properties (parameters). It is planned in the upcoming revision 1B of API Blueprint – as discussed in https://github.com/apiaryio/api-blueprint/issues/25Elan Dubrofsky commented
It would be really nice to be able to include descriptions of each parameter in a structured way, instead of having to come up with my own design using the overall markdown description.