30-06 case is very good already, I think.
My only temptation would be to blow it out and lengthen it as much as can be, and still fit in a standard length action. But that's been done by Winchester when they made their 300 win mag (regardless of belt). But then you lose one round in normal mags...
A 40 degree Ackley AI on an outstanding "re-standardization" of the 30-06 though. I have a 25-06 AI, and seeing an AI case next to a standard case just leaves you wondering why the heck things weren't done like that in the first place across the board. The military history of the 30-06, and the need to feed in machineguns, I suppose. In modern firearms, straight walls and a 40 degree shoulder with a medium length neck just seems to be the only thing that makes sense...