How about: If a patent is not implemented in a marketed product within two years (for a mechanical product) and 4 (or 5 years for a chemical product), the patent is void. In other words, no more patenting things and then sitting on them and suing others. Also, only certain entities would be able to patent something and then license it out (like the government, universities, legitimate research outfits, etc.).
Just thinking off the top of my head here.
I think that cure would be worse than the disease. It'd be a major incentive for large companies to say "no thanks" to small inventors, knowing that they can just copy it two years later.
By definition, patents exist to prevent competition. If you build a product, it should compete with everything else. If you can't stand competition, get out of the way of those who can.