Latest versions contain a automatic conversion from DataGrid to DataGrid2. Since this is a piece of logic, Mendix could provide this as a tool "Convert all DataGrids to DataGrid2"
The other option is to write an modeler extension for this, a lot of work and the same as above, but may be customized for your app.
3rd option is to do this via the Model SDK.
I would prefer the first one and file an idea for Mendix.