I think price is increasing because of the upcoming forks and no one want to miss this opportunity so they are buying bitcoins leading to this surge in price. But the main thing is what happens after the fork, will bitcoin price go down or will it still stay at this price, what I think is that it will come down due to mass selling.
Fomo is real no doubt about it. They are all anticipating that the upcoming forks will give them free coins from Bitcoin gold. So everyone is jumping onboard and don't want to be left out because the steam has started to roll and we don't know when the train will stop.
As far as sustainability is concern, we can't say it for certain. If they are willing to stay on, or will they go back to altcoins. (specially those who have sold their altcoins and bought bitcoins), remains to be seen. But based on experienced with the Aug. 1 split. After the dust have been cleared, the price remains steady and didn't go down as one will suspect. So I believe this will repeat with the current situation. No major dip, but the price moves on side way. Let's see though it we are going duplicate everything after Oct. 25.