What is the point of this then? Tableau can directly connect to most of these data sources already. Is this meant as a replacement for a data warehouse to take transactional information into a format that is quicker to report on?

EDIT: After reading into this more it seems like Quicksight is Amazon's version of Tableau and connects to SPICE which is Amazon's version of a data warehouse. If you prefer Tableau, you can apparently connect that directly to SPICE. If you already have Tableau connected to a data warehouse, this would appear to be a new competitor to the market and wouldn't add anything to your specific setup (beyond Amazon's claims that they will do it better).