What's next after AJAX?

(Via Infoworld) Rohit khare writes there are some capabilities that Web-based apps can't handle - yet. Excerpts with edits and comments:
While it may be right that the rapid spread of the term AJAX (asynchronous JavaScript and XML) - from Weblog to Wall Street Journal within weeks! - might lead developers to assume it’s a breakthrough that heralds the death of desktop applications. The recent spate of new Web applications under the AJAX banner have redefined end-users’ expectation of what’s even possible within a Web browser by offering smooth scrolling, incremental updates, and more responsive input forms. Nevertheless, so-called fat-client UIs still retain one fundamental advantage over Web UIs: real-time event notification. AJAX alone does not address IM, stock tickers, and other collaborative applications that require “push” data streaming. The key goal of AJAX-style applications is to decompose jarring transitions that download an entire new Web page into a series of smaller, more frequent transactions. Developers consider AJAX to be “asynchronous” because data can be updated without interrupting the user. In the middleware community, however, the formal definition of asynchrony refers to the capability of sending a message at any time, in either direction. AJAX provides the upstream direction, but HTTP would appear to make server-initiated transmission impossible.
Manuel Kiessling’s open-source ARSC (A Really Simple Chat) uses AJAX techniques to send input lines upstream, whereas a modified HTTP server that holds open thousands of simultaneous connections rebroadcasts the chat stream to other users. The subtler and broader implication of combining AJAX with asynchronous event notification is to extend publish-and-subscribe application integration across the Internet.
The clear benefits of migrating desktop applications to the Web in terms of maintenance, security, and scalability must be weighed against the costs of slower response times, limited interactivity, and less-than-beautiful graphical interfaces. With AJAX, push technology, and the ubiquitous plug-ins for PDF and Flash, the Web is closer than ever to becoming a viable default platform for application development.