Sword of Once and Future shows up in a lot of EDH decks, but not coherently aside from Mirko, Obsessive Theorist
After some testing of this card, I can report that it is simply worse than Mana Short
The way it works, is when Thassas Oracle enters the battlefield, you get to look at the top X cards of your library, where X is equal to your devotion to blue (how many blue mana symbols appear in the casting cost of all permanents you control)
Then when it does damage to the player, it gets a counter making it even bigger
Since they control it, they view the card as weaker, which means it stays out for longer
In limited, you have enough Lander tokens floating around to repeatedly double somethings' power, but in constructed and Commander, this slots nicely into the endless parade of fetchlands, extra lands, and land recursion that already make land decks an absolute beast to play against