I do a lot of Microsoft SQL development and can see some potential there - it's easy to tweak values in a database without leaving a trace.. so with some audit trail triggers any change could be logged, hashed and put on a blockchain.   And something like what SIA coin does for the backups, which is a distributed, encrypted backup..

The problem with relational databases is they are usually full of really private info, so there would have to be some strong measures in place to ensure it can leak the data or have security issues.