[takeda]

This appears to be a desktop application, so SQLite seems like a good fit. Although if some people are requesting it perhaps they have their reasons. For example if I had RDBMS already setup with proper backups I would generally prefer to use that, since there's no effort to make yet another allocation use it. It most likely would also enable me to have access to the same databases from multiple computers. With SQLite you would have to solve the same problems again (e.g. store the database in Dropbox account, and deal with shortcomings of that approach)

IMO instead writing how SQLite is the best choice for the project I think it would be better to add support for multiple backends. Something that is good for you and majority of users does not mean it's good for everyone.