Don't know why this game doesn't have it already, but we should have artifacts in the ground to dig up for various reasons (cool find, resources etc..) Imagine digging and finding things like dinosaur bones, ancient ruins, ship wrecks and even ufo crashes. If you can think of more, post it or forward it to notch :)
Ufo's are just fun, I love mining, and it'd be cool to find other stuff than a chest with monster spawner (found loads on the same seed) I'm currently digging out the entire ground which is easy considering the cave system covers the whole underground. I've spent ages so far, its overwhelmingly huge but the stuff to find isn't too exciting and some cool discoveries would be great to use as way points for when I get lost etc... Although I'm sure nitch can find a purpose for these additions.
I agree, random cool stuff to find while excavating would be sweet. And you can never have enough UFOs...they could be loaded with rare ore or something. But yeah, unless this is added on the PC first, it likely won't be added to the 360.
The next update is pretty much already set, and so are all future updates. The entire goal of the updates we'll be getting are to bring the Xbox Edition of the game up to the same level (or as close as possible) to the PC version of the game. Since there is a lot missing from the Xbox Edition, 4J Studios pretty much has their work cut out for them. Once the updates are implemented there will be more stuff to find, though I don't exactly see the purpose of artifacts and other similar items given that Minecraft is about what you can create. Although you may be pleased to know that in the future there will be abandoned mines and NPC villages as well as new monsters and golems.