So far the consequences of Barry’s time traveling in The Flash Season 2 finale and the Season 3 premiere has strictly been limited to changes affecting him and those closest to him.
Obviously it would have been great if such a change on TV had occurred directly after The Flash Season 3 premiere, but admittedly, that might have confused Supergirl viewers who aren’t keeping up with the other DC shows.
Well, maybe Barry, but I suspect he would have kept that nugget of information to himself.
The crossover, then, would have been the next best alternative.