In addition to increasing the bandwidth from 18Gbps to 48Gbps, allowing for 8K at 60P and 4K at 120P, and improved audio handling, the new 2.1 HDMI standard improves dynamic range and HDR potentials significantly by allowing scene by scene settings rather than a global setting at the start. See this article for more.
At least, that’s our opinion.
For sure, anyone buying 4K needs HDMI 2.0, and if you are buying an inexpensive TV not capable of displaying a high dynamic range (HDR), then you can forego HDMI 2.0a. However, if you’re going to buy a 4K TV and you want HDR (which is probably more important than resolution), then you should wait to get a TV with HDMI 2.0a, as this new specification is all about the transmission of HDR formats.
Presently, only the new, high-end 2015 TV’s have, or have the potential for HDMI 2.0a. But more and more will get this capability, and some of the current 2015 TV’s will be upgradeable.
HDMI 2.0a has very little to do with the HDMI cable; HDMI 2.0a is about the electronics in the TV that output the signal that goes to the cable.