One challenge would be maintaining the native mobile platforms. Because of local storage limits on HTML5, I think you need to use more then the stock browsers on get it done.
Kexi picked SQLite as the default backend in 2004, and it was a good bet. For native mobile there's Qt Quick for the GUI with which large part of Kexi is compatible. A database creation/handling layer has been extracted years ago and now it matures under name KDb: https://community.kde.org/KDb