So… please correct me if I'm wrong here. I'm trying to get my facts straight.
On 8/1 it's quite possible that the majority of hash power will not signal for segwit (I think this is quite likely), leading to two chains being created. If this happens, then both chains start with identical difficulty.
Let's assume the segwit chain has a small amount of hashing power (say 10% of the total), so block times go through the roof. Difficulty only adjusts every 2016 blocks, so it will take awhile for the block times to come down, assuming there's no change in hashing power. For example, if we're doing a block every 10 minutes today, and we drop to having 10% of the hashing power, then a block will take 100 minutes. This will continue for 2016 blocks or 140 days, worst case.
Am I thinking about this correctly?
Also, when the difficulty does adjust, would it adjust enough to make 10 minute blocks a reality with a fixed amount of hashing power? Or is there a limit to how much things can change every 2016 blocks?
In any case, how could the segwit chain possibly be usable with such high block times? Sure, if it gets even a significant minority of hashing power it might not be so bad, but what's the ideal scenario here – ASSUMING the majority of hashing power doesn't signal segwit on 8/1?
Also, assuming we start with a small amount of hashing power on the segwit chain, what incentive do miners have (aside from the standard block reward + fees) to mine segwit blocks?