I see it as pretty weird that there would be entirely new gym leaders, because if I remember correctly, B2W2 only takes place a few years later. Now if you compare that to all the Kanto gym leaders that still were there during G/S, (except for Koga who became part of the E4 in Johto), where that took place like 10 years later or something.
But other than that, I'm liking the designs of the new gym leaders (and the protagonists). Also Alex, I'm pretty sure all the gym leaders will be replaced, and much of the region will look different due to the damage that Kyurem presumably will make. Alternatively, Unova might've been bigger than what was seen in BW, so it might take place in another part of Unova, and you get the chance of returning to the old Unova like with G/S/C, where you could go to Kanto.