Suggestion: When an island is hosting the seasonal sale, the corresponding mirror island should be 50% off.

Mirror island sales happen like almost never. Which is really annoying.
So I would suggest when all the monsters are available on an island during its seasonal sale, that then is corresponding mirror island should be 50% off.
This allows players to plan it out with their gems. And its still far enough apart, so players have time to get enough gems.
This should not happen on the out of season event.
They could also do this sale for the normal island, for new players.
What do you think of this idea?