WebSockets will fulfill most of your needs, except browser compatibility (it only works on limited browsers).
But its use is really straightforward. If you can control which web browser to use.
Yesterday we successfully demoed a prototype Android app with a Seaside backend, it uses Seaside, REST, and live updates with WebSockets sent to Chrome running in a Tablet.
The whole stack is there for you to use* :)
Regards,
* Given the proper ConfigurationOf* :)