I would absolutely love to be able to add an external data source (RSS, XML, CSV) as a table type, and also be able to export an Airtable view to a XML feed. (You can kind of accomplish the latter using Raleway’s Airtable import plugin and then a Google Sheets to XML plugin, but it is a touch hacky)
Take a look at this Wordpress plugin which imports all entries in an RSS feed and lets you turn it in Custom Post Types: http://www.wpallimport.com
Imagine something like this for importing to an Airtable DB instead of a Wordpress DB - it could be really powerful.
I would imagine an external data source having to be its own table, where all imported columns would be read-only - though you should be able to add additional columns to do formulas etc on the imported data.