Oden wants Wano to open the borders cause he hope that they can welcome n assist the certain someone when he comes n it's obviously Luffy.

Remember when Crocus said "they might be the pirates that you have been waiting for, Roger".

In Marineford, Whitebeard said to teach " the person Roger have been waiting for is not you, Teach".

Then, Pedro said this to Carrot, " I think Luffy and his crew are the ones who our tribe and Kozuki family have been awaiting for centuries.

Unfortunately, Oden couldn't do it, so Wano remain isolated from the entire world. At the end of this war, I guess Wano would open it's border and Wano people would be ally with Luffy n co. They would assist Luffy n Strawhats in their journey.