Thanks to the new XContent abstraction, CamelCase are back. All JSON requests now support also CamelCase fields (such in the query DSL), and responses can be sent back in CamelCase fields with the addition of the `case` HTTP parameter (actually REST parameter) set to `camelCase`.
The main idea here is to support using DSLs in dynamic languages (such as Groovy) that use CamelCase as their naming convention. So, if you are using Groovy, for example, the query DSL can include "constantScore" as a query, on top of "constant_score".
Note, this does not apply to the actual indexable source. The same JSON indexed will be returned, with the original casing.