MicroSD cards are about to be released on the SSDs. The new cards are relying on the PCIe and NVMe interfaces commonly used on modern SSDs
For comparison, Western Digital's new 1TB SanDisk microSD card, so announced at MWC and which claims to be the fastest 1TB card in the world, tops off at just 160MB / s for reading data, and 90MB / s for writing it. The new microSD Express spec so would crush (in theory) smaller capacity cards, like Delkin Devices' 128GB Prime card at a maximum read speed of 300MB / s.
The SD Association actually first announced full-size SD Express cards of the SD 7.0 specification, but today's news at MWC (the SD 7.1
Of course, for both the SD and microSD card sizes, we still have to wait for card manufacturers to start making memory cards that use the new specification as well as for laptop, camera, phone, and console companies build hardware that can take advantage of the faster speeds. But if you've ever read how long it took to transfer files to a memory card, a faster future looks closer than ever.