It's only part of the story WRT music copyrights. These are the sound recording rights, signified by the (P) mark.

At the same time there's the traditional (C) copyrights in the song itself, and these, as usual, don't run out until death+70. So Cliff isn't suddenly going to starve when his (P) sound recording rights expire. Not that that's a compelling argument anyway, since Cliff has as much opportunity to invest in a pension as anyone else.

"Bringing sound recording rights into line with copyrights" is totally disingenuous, since creation+95 is just as different from death+70 as creation+50 was. If it were about making the licensing maze simpler, we could have just gone with something easy like creation+100 for both and at least we'd know where we stood.

No, the reason for this proposal is to please the music industry lobby, primarily the Big Four record labels that own the majority of the rights. They knew when they were paying to have the recordings created that they would have 50 years to profit as rightsholders; this is the contract between the creator and the public that copyright enshrines, to promote the creation of works that will eventually end up in the public domain. Instead the public domain will be cheated out of the music it was promised when that contract was made 50 years ago. Not just the tiny proportion of the music of 1958 that is still commercially viable today, but all of it - and that leaves the public much poorer.

So change the terms of copyrights if you like, but a retroactive increase in copyright is a gift from the public to the music industry from which we receive no benefit, and should be opposed.