I agree with you to an extent, but I think the timeframe will be MUCH longer. I can't imagine difficulty increasing 10x over the next 2 years without a corresponding increase in price.
Thats because you still havent accepted the fact that production cost of asics is on the order of 100x less per GH than FPGAs. Its a much bigger jump than from cpus to gpus.
Now how long it will take for difficulty to go up that much and BFL thus having to cut their price correspondingly will depend mostly on a three things:
- BFLs pricing strategy. If they are confident they will retain a monopoly for some years, they may chose to start at current prices per GH and lower prices slowly and milk the market slowly. Think ArtForz gpu mining by himself. In that scenario its perhaps possible miners will earn their investment back, although by my reckoning, only if BFL prices their products well below what the market will bear or voluntarily limit their sales and price drops instead of maximizing revenue. Not something Id want to bet a lot of money on.
- How many people think like I do and wouldnt even consider buying something with more than, say, 3 months break-even. IF almost everyone thinks like me, ironically, the few ones that dont could mine profitably. However, given that nearly no one seems to agree with my point, and that price/difficulty will be determined by the highest bidders, this doesnt seem very likely. Looks like everyone is lining up to order.
- Appearance of an ASIC competitor. If, or rather when that happens, well things will go very fast because BFL will not only have to ensure their product is seen as a profitable investment compared to difficulty, they will have to price it against their competitor too. As always the result of competition is that prices (in this case, per GH) will approach marginal costs much faster, and remember how much lower they are than today.
The thing to note here, is that all of these factors are completely out of your hands, and your mining profitability will be at odds with BFLs profitability. Which one will you bet on?