I seriously doubt that SHIELD will be even the least bit useful.
Almost all patents are "valid" in the legal sense, and there isn't much present work to change the criteria.
I hate the "abuse" of the patent system, but let's be honest, trolls are not "abusing" the system in the legal sense. They have valid USPTO patents that generally stand up during review.
The solution is to change the USPTO patent process. Leaving this to the courts is nonsense. Most patent disputes are settled out of court, and SHIELD wouldn't fundamentally change that. A defendant primarily considers two things when deciding to litigate or settle: 1) likelihood of winning (either no infringement on a valid patent or no infringement because the patent is invalid), or 2) likelihood of decreasing liability by settling vs. litigating (i.e. will it be cheaper for a settlement or litigation + judgment).
I don't see how SHIELD changes either situation in any meaningful way.
Defendants in patent suits generally lose or settle. It's that simple. If there isn't a drastic change to the likelihood of a not guilty verdicts, I don't see more suits going to trial, and consequently, any chance for SHIELD to make a difference.
In my opinion, this is a typical useless lawyer solution. The idea is to increase the number of patent suits that go to trial and increase the incentive (i.e. money) for lawyers to pursue such trials. We'd make lawyers even richer, but the actual defendant won't be much better off.