JSON and XML templating system for API with autoconverting to camelCase in JSON case

I like the idea of some format-agnostic DSL that allows to describe data which can be automatically represented in several formats like JSON and XML.

I'm looking for something like rabl (or rabl-rails) that supports JSON and XML and simultaneously supports auto-converting names to camelCase from snake_case as for example jbuilder (only JSON solution) is able to do.

P.S. There is old issue on rabl, but it is still open.