I may be wrong but I think this is a play on words - for a while in the US we referred to Generation X, or "Gen Xers," who if memory serves were twenty-somethings, younger than the baby boomers, more cynical, more brand-aware, there was a host of qualities that this generation was supposed to have that advertisers and merchandisers had to court in a completely different way. Here Pepsi is saying that their particular formula for carbonated, acidic, high-fructose-sweetened, cola-flavored water belongs to not just Gen X but "Generation Next" --- the
future.