The patent pledge doesn't fix every problem with patents. It won't stop patent trolls, for example; they're already pariahs. But the problem the patent pledge does fix may be more serious than the problem of patent trolls. Patent trolls are just parasites. A clumsy parasite may occasionally kill the host, but that's not its goal. Whereas companies that sue startups for patent infringement generally do it with explicit goal of keeping their product off the market.
I like the idea of introducing private solutions. I've personally worked on a few. An underlying problem is that the economics of innovation are quite different for different technologies, so even if the law applied the same way (which is doesn't; claim construction is rarely an issue in claims to chemical compounds), the balance between stronger and weaker patent rights would be different.
It's worth noting that the pledge wouldn't affect any of the litigations I currently work on, or even any litigation I have ever worked on. Patent infringement lawsuits against startups (not founded by non-former employees) are a very recent development, which can be linked to the large-scale aggregation of patents by non-practicing entities over the past ten years.