The problem with creating courts or other bodies to rule on executive privilege matters is that the Executive still controls enforcement of any court Order. Sure, it might not look good if the President were to order his subordinates to ignore a court order, but keep in mind that the President would have already ignored Congress' attempt to acquire the information. Why should ignoring another co-equal branch matter? Would Congress really impeach a President over Executive privilege?

In our system, the Executive always has some degree of discretionary power that Congress and the Courts can do little about legally. Executive privilege seems to fit that bill. This is not a case for the privilege or against it, just reality.

If the proposed law passed and the President refused to comply with the ruling, congress could use contempt proceedings, rather than impeachment, if the law was written appropriately. Still not a perfect solution, but at least it isn't complete overkill.