How is ExecuteSQL different from SQL plugins?
FileMaker's new ExecuteSQL function works with the same internal SQL the plugins do: this SQL stuff has been part of FileMaker since ODBC was introduced.
But while FileMaker chose to only expose the Select statement in its function (and only some of that), the plugins can use ALL of FileMaker's internal SQL including Update, Delete, Add Table, etc.
Powerful stuff to be sure.
If you want to play with this, grab the free SQL Runner plugin from Dracoventions and jump in.