I know that this has been discussed in various threads, but I didn't find a formal feature request so I thought I'd add one.
A native JSON parser in the Roku would be really great. XML is versatile, and all, but it's incredibly big "on the wire" and a pain in the neck to parse, event with the built-in support. I do a lot of web work with lots of AJAXy functionality and always use JSON instead of XML (I guess that makes it AJAJ).
I'm currently working on a channel for a client and their video host prefers to deliver metadata in JSON and discourages the use of XML.