The real question to answer is "shave two minutes off WHAT"? It's pretty trivial to make a shoe that can shave 2min off of a marathon done in trainers just by making it lighter. Your average trainer weights ~11oz, and high-end racing flats weigh ~4oz. 7oz is 200g. Scientific research shows that every 100g of mass on your foot translates to a 1% increase in oxygen cost, which might be where Salazar is getting this two minute figure (~1.6% over a 2:05 marathon, not counting that oxygen cost is not 1:1 with running time).
Of course, there's a lower limit on how light a shoe can get. Go too light, and you don't have enough cushioning underfoot, and you actually become less efficient, for a few reasons which I won't go into now unless you want to hear more.
Anyways, what we are likely to see is an ultralight shoe that still has adequate cushioning for Mo Farah to run a marathon in, and tailored specifically for his feet. It could perhaps be well under 3oz, which, compared to a middle-of-the-road racing flat, would indeed shave (in theory) a substantial amount of time off of Mo Farah's marathon time, assuming the cushioning was indeed adequate for him.
The "tailored to his feet" part doesn't mean there's going to be any real biomechanical magic going on. It probably just means they'll fit the shoe to Mo's foot specifically. I remember reading about how Nike took X-rays of Bob Kennedy's feet so they could figure out where to put the spike holes on his racing shoes so they didn't push directly on his metatarsal heads. Silly, I suppose, but if you've got the money, why not? Similarly, Salazar had Nike's biomechanics guru make special shoes for Ritz which were supposed to fix all of his injuries—the shoes had variable stiffness in the midsole near Ritz's metatarsal heads, with the idea being to transfer less stress onto whichever metatarsal it was that was bothering him. Now, this is a lot easier to do with a custom orthotic than a custom shoe midsole, but again, if you've got the money, why not? Maybe in Mo's shoe they'll put a bit more cushioning under the forefoot because he has a "loping" stride, or maybe they'll position the rubber on the outsole to give him maximum traction based on his plantar pressure distribution while running. I dunno. What I can say with reasonable certainty is that there isn't going to be any groundbreaking technology revealed in this shoe.
Now, we can always dream. Maybe Nike has secretly spent millions of dollars developing a real breakthrough, like mechanical cushioning (instead of what we have now, which is viscoelastic cushioning). Maybe this new technological breakthrough will debut with Mo at London and he'll run an incredible time. But I wouldn't get my hopes up.
More reading on shoe weight, cushioning, and efficiency:
Franz, J. R.; Wierzbinski, C. M.; Kram, R., Metabolic Cost of Running Barefoot versus Shod. Medicine & Science in Sports & Exercise 2012, 1519-25.