Never? I don't believe the government withholds stuff for more than 100 years. Historians are already looking forward to getting the dirt on the abdication in 2037.
Who is still holding secret files?
Don't you think it's strange that, in 1988/9, there was never a big "show and tell" about everything that had been held back all that time? People seem to have been satisfied with the "Boss" letters and such stuff, but if you try and access or enquire about detailed police reports, suspect lists, and anything else that's supposed to be in the public domain, you'll find yourself running around in circles. I remember, years ago, mid-90s, trying to arrange an appointment with the National Archives to get a look at the list of suspects, which would have included dates of interview and transcripts of most of those interviews, but despite my genuine reason for wanting to take a look (I was helping a writer do research for a lecture tour), I was told the documents were not available for "casual perusal". What reason would they have for not wanting people to look at them?
All that happened in 1988, was that the Met/Government/Shadow People let out enough stuff to send the theorists off another fifty years of happy sleuthing, and they could breathe easy again. Chuck us a carrot, and we'll happily go munching. I have no doubt at all that there's a very big vault somewhere with stuff in, not just to do with this case, but many other "causes celebres", containing info that's just too sensitive to ever reveal, mainly because it will expose shortcomings in the investigations, corruption (inevitably), maybe high-profile suspects and other 'touchy' information that could have come out inadvertently. We only ever know what we're told, and there's never, ever been such a thing as full disclosure, it's an impossible concept. The notion that a government would just hand over stuff after 100 years, because it's the legal thing to do, is naive. Since when has any government governed by the law?
My own opinion, is that JTR's identity was known at the time but, for whatever reason, it was kept secret. If he did stop killing at the end of 1888, I think it's because he died/was killed, but I think the press and the (higher) authorities were happy to let people think he was still about. The political and social climate of the time was volatile and fractious. With JTR caught or killed, attention would have returned to the real issues of poverty, immigration, unemployment etc that the government of the time was hopelessly failing in (no change there, then). Their collusion with the press over the whole JTR hysteria is well-documented, so it's not beyond the realms of possibility that they also conspired to keep the Bogeyman front page news for as long as possible, even after they knew there was no longer a threat.