QAbstractItem model using qsizetype

I'm using QAbstractItemModel to render to a table the contents of a file on disk that is many GB in size. However, from what I can tell, I won't be able to model using more than 2^31 rows with the current definition of QAbstractItemModel::index() being `int` based. Seems to me that converting all of those `int`s to `qsizetype` would be straightforward but obnoxious.

This would (obviously) have implications for QModelIndex and a buncha other classes, and (I imagine) would need to wait until Qt 7.

Is now a reasonable time to contemplate such a change?