After testing out Wavemaker, I found one of the coolest features I've seen for a RAD platform. Basically an API wizard that allowed you to plugin a few settings, match some fields from your database, and get the resulting API data result as a new virtual table.
This page details the setup process on wavemaker:
In filemaker, I would see this as an augment of managing external data sources. Providing an API endpoint URL, username and password and/or access token; Mapping fields from filemaker required to complete the request.
Then the data source, with the resultant fields (auto-parsed into records by filemaker), would be available as a TO in the relationship graph, or as a data source for the Import Records script step.
This would replace about 90% of the work I currently do with API integrations, negate the need for plugins and manually parsing JSON results.