A similar sort of thing is already possible using the NOLOH PHP Framework (
http://www.noloh.com) using its Listener Control. Using a quick example similar to the post you can simply do something like:
http://noloh.diffpaste.com/#/691/. Furthermore, you can specify the various options, whether it's stream, short-poll, or long-polling.
A video demonstrating it from this past March's Confoo web conference can be found here: http://www.youtube.com/phpframework#p/c/C102458C2FFD8ACF/7/8...
We're also planning to add a more direct syntax in the future so that you can easily set properties of objects directly to a changing data source without having to handle the assignment in a controlled callback, which we initially mandate due to taking the cautious route, thus allowing you to handle for data and security issues.
Disclaimer: I'm a co-founder of NOLOH