Good writeup, but I'm wondering: was Colorless Eldrazi showing up because it's actually good, or were people just playing it because Shops was bugged on MTGO and this was the closest replacement?
I'm not sure what the timeline for the Shops bugs is/was, but clicking through to the tournament the sample Eldrazi list is from (Vintage Challenge on May 9), two Shops lists did do better than it. I'm inclined to go with "actually good, but maybe not the best at what it does, but also not very hated in sideboards at the moment."
It it just to protect it from artifact removal?
I think it has to be this. In theory it makes sense to me--if the reason to play Eldrazzos instead of Shops is to dodge artifact removal, you might as well run the creature-land that doesn't turn that removal back on.
@Thiim is probably the definitive authority.
The reason to play Eldrazi over Shops is likely a more favorable PO matchup and immunity to a lot of hate. You get maindeck Null Rods and their Hurkyl's Recalls are only a partial Upheaval against you as it leaves your clock intact. Most Xerox decks are also RUG and Bolt is not as effective in this matchup as Swords (and most removal targets artifacts).
The downside traditionally is that Shops tends to just go under you and the deck is much less consistent without a land as powerful as Mishra's Workshop. I've had success aggressively attacking the deck's Sol Lands with Wastelands and artifact mana (ironically instead of spheres) with otherwise ineffective artifact removal. Oh, and Infernal Reckoning is a great card if you expect Eldrazi. Your results might vary.
The Mutavaults are almost certainly an effort to dodge Grudge and Wear/Tear.