They didn't give out the pci-e 4 spec in 2011, they finalised the spec and gave it out in mid 2017 and it's coming to market well, actually in products like Radeon VII around 18 months later. In 2011 they just announced they were working on it and the planned performance, etc. It wasn't anywhere near finalised. It's like AMD announcing Zen project starting in like 2012/2013... the intentions were announced but they actually had to do it.
PCI-e 5 was finalised a month or two back and as such I'd expect products end of 2020 to mid 2021. For a gpu for instance it's far easier to add pci-e 5 compatibility than it is to add it to a full platform. So maybe gpus late in 2020 or early 2021 to have pci-e 5 support while motherboards/cpus that also support it to be mid to late 2021.
i only said they gave the specifcations in 2011 not that it was finalised then but when pci express 3 come out i could be wrong on this but i belive msi was the first motherboard to comeout with it g85 i belive it was BUt the forums i was on they all keeped saying That pci express 3 was pointless no gpu at the time could fully use the extra speed and that pci express 4 was also around the corner etc
I think your predictions are right about pci express 5 being about 2021 But i do think the ssd chip makers and controllers will push for it a lot more then previous revisions so they can keep pushing forward with the speed of the ssd