AJAX based Poormanscron

I've been thinking of a good fallback for running long-running processes on commodity hosting for indieweb social web apps. Given the special use case of social web apps, where users might stay on the app for a long time (or leave a window/tab with it always open), an AJAX based poor man's cron might work very well.

References:

• Poormanscron (Drupal module, Ajax based)
• Web bugs for job scheduling: hack or solution?
• AJAX Refreshing RSS Content
• Event Scheduling
• phpJobScheduler