Re: Reasons for traditional HD
yup, m.2 is the current answer
Samsung have a ~$500 512GB m.2 SSD out that does 1000MBps read and write, you will need a 15-30 dollar adaptor to fit in a regular PCIe slot though (needs v2 4 lanes).
More are coming, wait until the end of next year and you'll get your economical PCIe blazing storage fix.