First let's start for the people who don't know. In Emerald, there is a move tutor who teaches Sleep Talk in Fortree City. This will likely be like G/S/C, where almost everything learned it.
This may seriously change the metagame, but most standard movesets have changed and are better than in G/S/C. For example, the Raikou standard set is now better because Calm Mind exists. If we started to use Rest+Sleep Talk again we might not have enough room for needed moves. The old Raikou standard had Thunderbolt, HP Ice, Rest, and Sleep Talk if my memory serves me correctly. Will Sleep Talk be used again, or will it just sit and die? Discuss.