If you have a patent, you MUST have a product or be working on a product using the technology in question or you cannot litigate others using your idea.
That doesn't help in the case where non-innovative patents are used in an anti-competitive manner. Such as the patents Apple is asserting against HTC.
Sure, it may not help in THAT case but it would help with people hoarding patents for the sole purpose of suing others. There isn't going to be a single solution that solves the patent problem. It will be a combination of rules like
1) you must have a product on the market using the patent
2) no business method patents
3) software patents are limited to 2-3 years
etc etc
The problem with "must have product in the market" is the same as with the idea of fixing the domain name system by adding a requirement of "use it or lose it".
Who gets to decide what "having a product in the market" means?
It's impossible to generalize this to an objective set of rules. Thus we'd soon be back on square 1 (read: in the court room).
That doesn't help in the case where non-innovative patents are used in an anti-competitive manner. Such as the patents Apple is asserting against HTC.