Sort of, yes. Fivetran has a product called Powered by Fivetran which is an API on top of Fivetran that lets users connect their apps and push to a warehouse managed by you. For example, you could ask users to connect their Salesforce via Fivetran and the data would end up in a BigQuery dataset you own.

Although Powered by Fivetran could be used for the use case we're building towards, it only solves the "getting data out of Salesforce/Quickbooks/etc" part of the problem. Often the harder part is actually extracting the relevant data and working with it after getting it from an API.