We're getting ready to add JSON output format to NCBI E-utilities, and would like to solicit community feedback.
Please see the GitHub repository https://github.com/Klortho/Eutils-JSON for a very preliminary stylesheet that converts the existing XML format into JSON, as well as a few sample output files.
Let us know what you think, and send your comments and suggestions either here in the comments, via GitHub pull requests, a github issue there, or send an email to email@example.com.
We will be implementing this very soon, so don't delay. Send us feedback as soon as possible (preferably by the end of November, 2012).