1.5-2 years seems like a good estimate.
As you said, it's not like they need a price drop to spur demand. The supply has only now started to stabilize, and it's still sold out in some countries. Plus it's at a good price to begin with, unlike the PS3.
Really, though, I'm surprised that the PS1 dropped in price that quickly. I don't remember that at all (although I was only 5 or 6 when we got ours).








