They should have given us snowy Lorelei with festive decorations for Christmas. Just as they gave us Haunted Lorelei for Halloween und later on normal Lorelei with Marie Rose. But that would be too awesome of an idea and even make sense.
Actually don't seem to me a good idea, because TN would use a winter Lorelei for filling the (very likely) last empty slot for a stage (indeed it's pretty likely that Original Lorelei will be treated like a different stage filling one of the two empty slots). And also in the case of a snowy variation of an already existing stage, would be a better choice to use anyone less Lorelei, otherwise the game would end to have three different slots for the same stage.
The ideas over for a change weather were thought for being considered like an alternative of the stage not in place of a different one (just like happened in DoA3 and DoA2U, on the opposite of DoA4 and DoA5U). Seeing the situation, would be better include a completely new stage for having a snowy one, like Koku An (2U version), White Storm, Snow or Ice Cave.