The more corner cases I fix, the fewer opportunities for the exclude selection model 😅

AFAIU it would only be for "select all", but for large datasets it would improve that interaction substantially.

Correct, but there is a number of conditions for the exclude model to be used:

if (
  !props.isRowSelectable &&
  !props.checkboxSelectionVisibleOnly &&
  applyAutoSelection &&
  !hasFilters
) {
  apiRef.current.selectRows({ type: 'exclude', ids: new Set() }, params.value, true);
} else {
  const rowsToBeSelected = getRowsToBeSelected();
  apiRef.current.selectRows(
    { type: 'include', ids: new Set(rowsToBeSelected) },
    params.value,
  );
}

I would have thought that both models would be equivalent, assuming access to the full row id list (though that implies modifying the row list requires adjusting the selection model).

Ok, so { type: 'exclude', ids: new Set() } could be interpreted differently:

1. All rows are selected (current approach)
2. All selectable and visible rows are selected (this is what you meant, right?)

Do you see benefits in (2) compared to (1)?

On another thought, there's a difference between (1) and (2) when interpreting this model by the developers to perform operations on selected rows.
In (1), an empty exclude model means literally all rows.
In (2), an empty exclude model could mean different things depending on the data grid state. So developers would need to convert empty exclude into include (?) model to be able to perform actions on the dataset.

With the above, I think we should proceed with (1).
What do you think?

Yes, I think (1) is the way to go. Both shapes of the model should be equivalent, which isn't the case for (2).

The more corner cases I fix, the fewer opportunities for the exclude selection model

It's not that it's not usable for the conditions that you've guarded for, it's that some of them might require building a non-empty exclude model. You'd need an equivalent getRowsToBeSelectedAsExclude() function. And there are some cases in which it could make sense to do that work. For example, if there are filters applied that filter a small fraction (or none) of the total rows, using an exclude model would be much faster than building an include one.

In (1), an empty exclude model means literally all rows.

Does this mean that even if some rows are restricted to be selected by let's say isRowSelectable prop, they'd be selected but not de-selectable from the UI, similar to this?

(Based on the assumption that although we are discouraging the usage of exclude mode with isRowSelectable, we aren't forcing it.)

@MBilalShafi Yes, this is the current behavior: