Without going into the debate with competitors too much - from what is observable from the progression in bitcoin mining IT is that gen3 equivalent hardware from AM and "next-gen" hardware will likely co-exist long-term (> 2 years). This is because there are 10-fold variations in energy prices dependent on location and still large bitcoin price fluctuations, which gives mining a timing value. As such one may expect the less efficient hardware to migrate into areas of low electricity costs and opportunistic mining, while high-efficiency hardware goes into high-cost areas (e.g. through supply and maintenance chain issues) and sustained mining. This will make the overall hashing power of the network much more elastic.
The bottom line is that while gen1 or gen2 ASICs may come to an abrupt death, the gen3 ASICs will likely fade out smoothly.
I agree with your end game prediction about hardware distribution and that gen3 will fade out much slower than previous generations but I don't think it will take 2+ years. The market will be flooded with 14nm asics by then.
Although there is a 10-fold variation in electricity prices, mining will only be feasible for the top few percent. It really doesn't make much sense to mine with $0.2+/kwh.