I see JSON becoming the dominant player in the AJAX world in the upcoming future. It's ease of entry, especially if bundled with PHP will make it a no brainer for AJAX or AJAJ applications.
"From: Rasmus Lerdorf
Subject: [PHP-DEV] JSON inclusion in core
Date: Fri, 20 Jan 2006 11:31:58 -0800
pecl/json is a rather simple extension with no external deps (it bundles the small library it uses). The JSON format is stable with no real possibility of changing basically by definition, and I see its use exploding this year. There is also talk to a JSON Request object being added to browsers and if that happens we need to support that natively much like we support url-encoded form data ending up directly in $_POST. I could see a $_JSON if browsers start sending this. But, as an initial step how about we bundle pecl/json in the next release?
There is an issue with the fact that it is LGPL'ed. But perhaps we can work with Omar to put at least the extension part under the PHP license when bundled with PHP.