I'm planning on upgrading to a new MacBook Pro with USB-C/Thunderbolt 3 and will get the dock, too. I travel to various client offices, so want the ability to quickly unplug-replug with the minimum of cables. I use it with a 2012 15" MacBook Pro Retina, a G-Tech Thunderbolt 3 RAID, a couple of LaCie Firewire 800 and Thunderbolt 2 hard drives, external monitor, keyboard, trackball, Ethernet for an 11x17 LaserJet printer. I have a Thunderbolt 1 dock from them and it's excellent. It will also power and charge up a new MacBook with USB-C/Thunderbolt 3. OWC makes a Thunderbolt-3 dock with an SD Card reader in the front panel. Most importantly, it has a pair of USB-C ports used to connect other devices. It is available in 256GB, 512GB, or 1TB capacities, and its speed is much faster than the old SATA SSD. Please note: this adapter is not suitable for wearing a protective case. GNARBOX 2.0 is an external hard drive with an SD card reader. I just googled for comparisons of TB2 docks and in the handful of articles that compared various TB2 docks, none of the docks had an SD card slot. 7-in-1 Multi-Function USB C Hub: Expand your MacBook ports into 3 USB3.0 + HDMI+Thunderbolt 3 and SD/TF card reader, this Macbook Pro Adapter is a great expansion for new MacBook Pro/Air that only have limited ports, certainty its made your office or life much easier. I'm pretty sure these were A/C-powered docks the expectation being that you'd use them for attaching and detaching your "stay at home" peripherals not for adding SDxC slots on the road.
There were several Thunderbolt 2 docks, aimed at Mac owners, that had SDxC readers, back in the (not long gone) days when rMBPs still had SDxC slots. That is because Apple discontinued SD card readers on a number of their products. Incidentally, two of the announced TB3 docks have SD carders, showing how much these docks are directly at MBP users, given that the MBPs with TB3 have lost their SD card slot.
Except for the fact that it appears that no TB2 dock with SD card reader exists. In principle, a TB2 dock with SD card reader would be such an insanely-expensive-for-absolutely-no-benefit SD card reader.