They don’t even have to use a 3.5 inch format to gain capacity. They could use 5.25 inch (the same as optical drives) Of course, a tradition HDD could also use a 5.25 inch form factor, but with that size of platter, access times would be very slow, not so with SSD. The only factor is cost of NAND flash memory.
Tradition HDD will be around for a while, as they are cheap and offer large storage. SSD in the other hand make great OS system drives. They leave all traditional HDD for dead when used in this configuration. If you ever fit an SSD as your OS drive, you will never want to go back to using traditional HDD.
I can’t wait to get hold of one of these new OCZ Vertex drives for testing.