Whether its adding another turn of Fogging to your Spike Weaver, taking the -1/-1 off your Woodfall Primus, or nixing an age counter from something with cumulative upkeep, there will likely always be a target for Quarry Haulers ability
Do we know yet or is this just an art leak
You can and will get mana fucked with reasonable regularity, there are insane combos that once executed you cant do shit about, there are trick decks that will annoy you and if you are in a rush to get your collection up, you can as always spend your rent money in short order
Not only can you use them for mana or find your colors when the opportunity is right, but if you draw them late in the game, you can cycle them away
Then when the dork swings you get a power boost equal to the top card of your library's mana cost, and you'll lose that life as well