As in all things aviation, if you change on thing, you end up changing many. There have always been claims that the wing was designed for the mythical -900, but I’ve never seen anything official that says that. It really makes very little sense, to compromise your design, for something that might happen in the future.
The aircraft’s performance was as good as it was, in large part because of the wing. It would never have been able to operate from the shortish runways that it could, had the wing been smaller. The large wing was also a factor in its ability to get up high, early in flights, which helped with fuel burn. Approach and take off speeds were relatively low, again because of that big wing. Make them higher, and you need more powerful engines, longer runways, and so on.
Engine reliability was an issue. Changes were happening far too often, though failures were rare.
That would give you an A340. Underpowered. Terrible performance. Probably unable to fly across the Pacific (west bound). It would have had approximately the performance of a 380 operating on three of the current engines...not nice. The aircraft would have been stillborn.