Thunderbolt & DisplayPort
Thunderbolt 3 has two DisplayPort 1.2 data streams
There have been rumours of a Thunderbolt 3 update, not the fourth version, but a smaller update to bring DisplayPort 1.3 into the mix - bring on Thunderbolt 3.1
Thunderbolt 3.1 could have a DisplayPort 1.3 data stream
Thunderbolt 3.1 would have the same PCIe performance as Thunderbolt 3
Thunderbolt 3.1 could have double the USB 3.1 performance of Thunderbolt 3
Thunderbolt 3.2 could have two DisplayPort 1.3 data streams
Thunderbolt 3.2 would have the same PCIe performance as Thunderbolt 3
Thunderbolt 3.2 could have double the USB 3.1 performance of Thunderbolt 3
There could be a second-generation Thunderbolt 3, think of it as Thunderbolt 3.1 for now
Thunderbolt 3.1 will feature DisplayPort 1.3
Thunderbolt 3.2 is likely to be an option, it will feature dual DisplayPort 1.3 like Thunderbolt 3 carried dual DisplayPort 1.2 streams
Thunderbolt 4 will feature DisplayPort 1.4
Thunderbolt 4 is the jump where we will see external GPU supported at PCIe 3.0 x16 or PCIe 4.0 x16 if available at the time of designing & engineering Thunderbolt 4