Single source of truth in one place is a paradigm that has scuppered many an EDW project.  Once an organisation gets beyond a certain scale you are on a hiding to nothing.
To start with define "single source of truth".  Is there a universally agreed truth?  Would the finance department agree with the sales department on what constitutes truth?  Does what constitute the truth change?

Does all the data within your organisation originate in your organisation?  Do you have control over all data in your organisation?

I'm finding that the source of truth for "products" resides in system 'x', the source of truth for "customer" details resides in system 'y' and the source of truth for a large chunk of reference data resides externally.