Storage medium is just part of the equation. The other important and hard part is the mechanism that is required to read and write data to that medium. Would you use a CD as a storage medium when the CD reader/writer is size of a washing machine?
Yes, according to history, if that's all anyone had. :)
IBM's project might be the ENIAC of molecular storage devices. Only time will tell. Keep in mind your example doesn't go far enough to match past history, we used to actually have much worse than 600MB / washing machine. We used to have 100 words / warehouse.
"By the end of its operation in 1955, ENIAC contained 17,468 vacuum tubes, 7200 crystal diodes, 1500 relays, 70,000 resistors, 10,000 capacitors and approximately 5,000,000 hand-soldered joints. It weighed more than 30 short tons (27 t), was roughly 2.4m × 0.9m × 30m (8 × 3 × 100 feet) in size, occupied 167m2 (1800 ft2) and consumed 150 kW of electricity."
"In 1953, a 100-word magnetic-core memory built by the Burroughs Corporation was added to ENIAC"
https://en.wikipedia.org/wiki/ENIAC
* EDIT: It'd be more fair to use punch cards as ENIAC's storage mechanism to compare against, and punch cards held a lot more than 100 words. Anyway, still, crazy by today's standards, right?
But to get back to your original point, a washing-machine-sized storage machine is perfectly acceptable if that's all your technology allows. In fact, it'd even be acceptable now, if it allowed you to replace what currently takes a whole data center's worth of hard drives. I'm sure Google would be ecstatic if they could store all of YouTube on a single machine the size of a washing machine.
The smart thing to do nowadays is to locate processing circuitry with the memory in order to reduce transport and maximize parallelism.