Not enough people have reliable broadband for online storage to be the future. And the broadband that is out there is getting costlier and less broad.
It would create a huge data bottleneck.
Look at all the engineering in the PM G5, and how not only the processor was massaged up to higher GHz, but how everything else was widened too -- hard drive, PCI slots, RAM speed, etc, etc. It's these things that truly make the computer fast.
It doesn't matter a whit if you've got dual 5GHz G6s under the hood if you're accessing your data from a 12Mbps USB hard drive, and for too many people, internet storage would be that slow or worse.
I think the future will be in a newer, higher density DVD sized disks and tiny, portable hard drives (connecting with FW800 and/or USB 3.0).
The CD/DVD size format has proven so insanely successful that the industry will have a nearly impossible time getting the market to accept anything else.