the only way to make this idea convenient for everyone without making it too OP and without affecting too much on the negative aspects indicated so far, is to make sure that this GMS does not tell you the nature of the pokemon but only tells you if your synch has worked or not. Let's assume for example Scyther: it can be played in many ways. If GMS tells you the nature, you could abuse all synch fail as well. If, on the other hand, you are looking for adamant and your synch fails you can decide not to take it, even if maybe it could be one of the other useful natures.