I can see the Norwegian style double threshold becoming more common at the top level, with runners at lower levels adapting more of the threshold intervals for lactate threshold training (2ks, 1ks and 400s with short rest) instead of the current model of tempo runs being continuous runs with no rest. Another innovation that could become more popular with the Norwegian style of training is only doing race pace work very close to competition, with threshold work being done year round.
The posters above mentioned cross training, and that seems like a good bet. Anyone could hop on a rowing machine for an extra 2 hours of easy aerobic work every week with no strain to the lower body.
Although neither of these would be innovations, just popularization of already known ideas. Realistically, the next big breakthrough will be some substance that will either boost aerobic capacity or reduce recovery time substantially. Maybe this already happened and thats why people have been running faster the last few years. Who knows?