Maybe... but a regular spreadsheet doesn't map very well to a RDBMS due to its variable and flat structure. It might map to a column data store like Cassandra I guess, wonder if anyone has looked at that?
What I'm working on though is more about taking the core of existing spreadsheets and building powerful integrations on top of it. Like in the sibling comments, building a webapp, or something else. I really think this has huge potential.