The designers of Scribunto decided to not allow Scribunto scripts to make API calls, as this would create network traffic during the page save process, which has the potential to considerably increase the time taken to save a page. Scribunto was originally conceived as a way to make the page save process quicker, so I doubt that the devs would be open to adding API support.
If you want to use the API from within the wiki, how about adding a JavaScript gadget? This allows users to access the API from inside the browser. You can also make the gadget load by default, so your users won't have to activate it in their settings. There are already scripts that do mass page editing, such as JavaScript Wiki Browser. (In fact, you might just be able to use that script as it is, without installing it as a gadget.)