PCI-SIG which is the organization that designs the PCIe express standard has released a roadmap to the public showing off the blueprints for when the next PCIe standard will be upgraded.
From the above image we can see that the PCIe 4.0 standard will be coming to us later this year and will be featuring 16GT/s which is a huge upgrade from PCIe 3.0 @ 8GT/s
What is really impressive though is PCIe 5.0 which is literally 4x more powerful then PCIe 3.0. PCIe 5.0 will be able to move 128GB/s through the PCIe slot which is massive when compared to both 3.0 at 32GB/s and 4.0 at 64GB/s.
Source: Tweak Town