Storage likely isn't going to be the issue as that traditionally has trended larger and larger.  Bandwidth on the other hand is more likely to be the real issue.  Most Internet connections haven't jumped up in speed over the past few years and unless some miracle happens for more people it will probably be the same speed in 4 years.  On top of that, more and more ISPs are instituting data caps on a monthly basis with insane overage costs.  Many of us who have been running a client all along won't feel the pain, but any new individual or business that is serious about setting something up will have to navigate the challenge of downloading the blockchain.

I like the idea of purchasing a multi-terabyte hard drive with a recent copy of the blockchain on it.  Plug it in, run a MD5 hash program on it to verify that it is legit and then only have to do a few months of catch up instead of 9 years...