Legendary is not a beneficial mechanic for ETG.
Why? I though it could provide for interesting effects and implement a "hero card" system that many people seem to like.
Once there was a legendary card type "weapon". Now it is no longer a legendary card type. People are happy about that change.
Ajit's hero card idea turned into a Totem Slot where each totem could animate itself.
Legendary leads to dead draws or is unreliable.
The closest ETG should get to Legendary is with something akin to MTG Grandeur keyword involved.