I don't know. These days, the only thing that makes my computer feel slow is the hard drive. The capacity of hard drives has been keeping up with or exceeding demand, but the speed seems to be increasing much more slowly.
I'm not sure why we're talking about a 250GB drive in 2020 anyway. SSDs are already that big (and bigger). They just cost a lot right now. While I will probably keep a disk based drive for storage for many years to come, my next boot drive will almost certainly be an SSD. The random access rate of my Raptor not only seems slow, but is very loud. I welcome the extra speed and silence of an SSD, even if it's more expensive.
Like you said, the price basically stays the same. The point that TimeOday was trying to make wasn't that 250GB SSDs would be available in 2020, but that they would be the commodity keychain drives that 4GB flash drives are today, and could be had for $20. Today 256GB SSDs cost $600 or so. In two years, 256GB will probably be under $200, and 512GB and 1TB drives will be $400 and $600 or so...maybe less. The point he was making is that flash drives have the capacity to be reduced much lower in price than hard drives can, because they don't need the complicated mechanical parts in a disk based drive.