It would be really great if you could support webservice requests in AJAX Callbacks. The APEX builder allows you to define many different process types under here but currently only executes PLSQL processes.
In APEX Debug output the following message is displayed: “process does not contain pl/sql code”
The following APEX forum thread also asked about the same capability: https://community.oracle.com/thread/3781895?start=0&tstart=0
I think many developers would benefit from being able to make the webservice calls via AJAX without having to resort to writing PLSQL which is time consuming and requires more maintenance.