Over four films we have seen a number of artifacts.

The two more successful films both had items that were easily recognized by western viewers. They were mystical, but grounded in familiar history.

In Temple and Kingdom we had two other items, both mystical, but not as familiar.

Now some might say Raiders and Crusade were successful because they were based on Abrahamic items. But I don't think this is the case. I think it was because of familiarity. If an item is just as familiar and historic, it should knock it out of the park, granted it's written well.

However, Hollywood likes global markets. So we aren't looking for something that will only interest the west. While I'd love a Spear of Destiny tale, another religious artifact I personally don't see being used.

Excalibur. A mythical/mystical sword of legend. Most of the world is familiar with Arthur and his sword, but the idea of a sword in general is what is important. China and Japan have a great many stories about mythical/mystical swords, so even if they aren't intimately familiar with Excalibur, they are very familiar with the concept.

Here we have an artifact that can capture the world's imagination. An item worthy of Indy risking his life for. And most of all, given the Nazi involvement, make sense.

So to me, Indy 5 is likely the Quest for King Arthur's Sword. (no, I don't mean that as the title.)