I don’t think they will ever become fully worthless. Once NC UCs drop, everything is going to shift, especially how TNT decides to release them. Without going into too much UC Release Lore, RN & RWs are going to keep increasing in value, BD pets may trade well, Y1/Y2 pets will go up, and perhaps “Old UCs” could hold new value.
Everything is up to speculation right now, but honestly, I’m just excited for more art =)