Traps are always being designed and suggested. They are also quite possible, but limited in scope. The thing to keep in mind is that they must remain on the basis that they do not need any interaction from the player once they are in play, so as to not conflict with the other player's turn.
To examine your suggestions, the 1st and 3rd would be perfect for a trap design, since it automatically activates the effect and targets the appropriate card without needing interaction from the owner. The 2nd seems to require a selection, though the wording is not quite specific on how it works, and may be a problem as a trap card in EtG.
EDIT: We already have some trap-like cards, such as death trigger effects. Also, most shield effects can be considered trap material, given they require a trigger of some type, such as creature and spell damage, in which they retaliate.