Yes, Linus himself mentioned they'd all need to be contacted and agree. He also said he saw the GPLv3 draft and so it was an early and conscious decision to not have a 'GPLv2 or later' license.
There were differences of opinion at the time. Eben Moglen said something to the effect that it could probably be relicensed on the theory that its history suggested it could be treated as a collective work. But it would have been controversial and Linus didn't want to anyway so discussions never went further than that.
Here's something I wrote at the time: https://www.cnet.com/news/linux-to-gplv3-a-practical-matter-...