Card-Forge
ETB RE of multiple Arsenal Thresher should still see all in hand
If Arsenal Thresher and another artifact are entering the battlefield from your hand at the same time, you may reveal that other artifact for Arsenal Thresher. If that artifact is a second Arsenal Thresher, you may reveal each Arsenal Thresher for the other.
This might be tricky, because right now the RE are run sequentially so that when you could reveal for the second the first is already on the battlefield.
Maybe we can somehow use restore snapshots for all the relevant information:
If one of these lands is entering at the same time as a "shock land" (a cycle of lands originally from Ravnica block that allow you to pay life or have them enter tapped), use the life totals of all players before choices are made for that shock land's replacement effect to determine whether the land enters tapped. For example, if a Lakeside Shack and a Breeding Pool you control are entering at the same time (perhaps because of the effect of a spell like Scapeshift), your life total is 14, and your opponent's life total is 20, the Lakeside Shack will enter tapped whether or not you choose to pay life as Breeding Pool enters.