I bore myself going on about this, but the old standing was safe, it was the fences that caused people to die. No one at Liverpool moaned about the old Kop being unsafe, quite the opposite in fact they revelled in it. The proposed system in my opinion just makes standing safer than the current situation, which is people standing in seated areas - I've injured myself far more often falling over onto seats below celebrating at Wembley, Chelsea, Palace etc.
The daft thing about this debate is that the old style terracing still exists in lower divisions and in other sports, with no problems, and more obviously, at stadium rock concerts where the entire pitch is standing with no barriers, with constant surging at the front (ultimately within a 'fixed space' with limited ways out at one end. Hillsborough was obviously an enormous tragedy, and has shaped the game for good, for bad, but the lack of atmosphere at football is down to pricing out teenagers and under 25s, and the embracing of the corporate dollar, nothing else. If safe standing makes a difference to that an is the only option, then lets go for it.