I am writing an RSS feed (for fun) and was looking at the spec here.
RSS is a dialect of XML. All RSS files must conform to the XML 1.0 specification,
You're right that the client reading the feed would have to have custom support for whatever the particulars of your JSON were. So you'd either need to make a custom feed reader to consume that information, or someone would have to propose a JSON feed standard, and it'd have to be widely adopted.
Well, I think your desires have finally been met, friend!
Take a look at JSON Feed. As of this writing it's only about a week old, but it's already picking up steam, having been supported now by Feedly, Feedbin, News Explorer, NewsBlur, and more being added all the time.
If I had to pick a standard to use when generating a JSON version of RSS, I'd pick JSON Feed for sure.