It's worth noting that there has been a Sheets connector for BigQuery since January, although only for G Suite customers: https://cloud.google.com/blog/products/g-suite/connecting-bi...

This announcement seems like an expansion on what's above (e.g. pivot tables). I've tested what's above for my org and there's a lot of promise. (only criticism is creating formulas in the query don't work automatically since they are returned as Text cells; workaround is to cast as Automatic)