That's currently impossible (to my knowledge) because API Blueprint encodes far less data than Swagger can. Moving losslessly between formats wouldn't work unless APIB changes...
/author of API Blueprint here/ I would not say this is the case. API Blueprint focuses on different data for various reasons (design-first, documentation-orinented). In order to bring the Swagger support we had to introduce some extension in the format. We are, however, trying to unify the tooling under the hood of the refract project (https://github.com/refractproject/refract-spec/blob/master/n...) through (de)serialization plugins for the Fury.js library (https://github.com/apiaryio/fury.js)