For context, this came out in 2016. SSDs were not yet the ubiquitous default, not by far. Many laptops shipped with HDDs or SSHD (solid state hybrid drive) for

For context, this came out in 2016. SSDs were not yet the ubiquitous default, not by far. Many laptops shipped with HDDs or SSHD (solid state hybrid drive) for faster storage. The most common SSD fit in the slot to replace these so they were 2.5" and SATA. Cheap NVMe as a category started to emerge that year but only H2 of it especially with the Intel 600p. Also, most laptops could only run them at x2 because the On Package Interconnect between the CPU and the PCH was set to 2GT/s instead of 4GT/s for better battery life. This made total sense: SATA only could use less than 1GT/s anyways so why bother? The other potential bandwidth hog was Thunderbolt 3 which did appear on Skylake laptops but most laptops used the Intel JHL6240 which only used two PCIe lanes instead of four once again for power consumption reasons and so they thought oversubscribing the 2GT/s link with SATA and Thunderbolt is okay. Even to this day the only semi-common high bandwidth Thunderbolt peripheral is the external SSD. The next year, in the ThinkPad T470 Lenovo will start selling what OP hacked here: it had a kit which put a M.2 key M slot inside the HDD bay and connected with the appropriate cable.