Cool idea. We've built a spreadsheet-powered web platform (Cloudstitch - YC S15) that lets you publish web forms and widgets that rely on spreadsheets as a backend.

Several folks use us just for the spreadsheet API -- as this service seems oriented. We provide a simple, common API that can talk to both GSheets and MS Excel 365, support various forms of row-level access control, and Ruby on Rails-like join syntax. Would love to hear feedback.