For now, it's impossible and likely to stay this way. It's also a good point that some coins which are presumed to be stolen might be unmoved for other reasons, a person has the right to not move one's coins. If you didn't touch the money in your bank account savings for 5 years, would you find it fair if the bank redistributed all your money to some random people? If not, then you shouldn't want the retrieval of "lost" coins either. Also, if one day it does become possible to crack the keys (say, due to huge progress in quantum computing), the moment it becomes possible Bitcoin itself becomes obsolete because the money isn't protected any more. So there won't be a point of retrieving something worthless.