There could also be the possibility that there is equipment out there can't actually solve a block now? What proof is there that all equipment is capable of achieving a best share in the billions and all chips and mining equipment is equal? We are told it can? But can it really?If so where's the proof?We are just left with X companies word?Many companies could of very well just made short cuts because no one would be able to prove they did and chalk everything up too luck? sha 256 only uses 128 bit memory bus @ 2^128 which is limited to about 16 Billion as a 32 bit address is just approximately only 4 billion @ 2^32 so  it is mathematically impossible for it too use every nonce numbered 1 to 16,800,000,000 at full capacity already it can't use every nonce so a short cut is already made somewhere?.
 I have read that there is equipment that is unable to use every nonce? This would make sense as a limiting factor?This might be the limiting factor on much of the equipment today? As earlier mining equipment was built with most likely a use of a limited amount of nonce's as it only needed to solve a best share in the millions and not expected billions?This very well can be the deciding factor of who solves a block or not? and why there is a lack of block finding all around? Because it seems to be clear cut across the network and not just a single pool.
 We should have a list of all the mining equipment and compare all companies and  the Best Share achieved on each equipment and which has solved a Block or not and with what if they did? I think then we will get some interesting  clear answers and find out some equipment might have never solved a block or achieved a best share in the billions?There might be companies that sold faulty equipment or just made short cuts on the nonce's the equipment can use?So now at this difficulty it is incapable of solving a block with difficulty so high? Something to think about it? As could very well be the possibility it's not the pools but the equipment we use?