Interesting but of course you would have to remove your microsd card to use it.
A USB hub allows you the flexibility to add both a HDD and a typical card reader or other devices. Some USB hubs include a card reader although I prefer a separate one. Good find though it will meet some peoples needs.
How about a microSD Hub, anybody make one of those?
Keep any eye out for an SP3 Power Port expander since the Dock Connects using the Power Port maybe a portable port expander will pop up. Preferably this would also have a Power Connector on it so the power adapter can still plug in, 2 - 3 USB 3.0 ports, additional DisplayPort, DVI & HDMI, microSD or SD slot, and the ultimate a pcie connector optional external GPU. Thunderbolt would just mean everything else you wanted to connect would be more expensive and no single device needs that speed.