Re-Logic has released a few spoilers for Terraria 1.3.6 (now 1.4). Chippy Gaming has some videos about them.
“Confusing” spoiler: https://youtu.be/Wr5lRQuaUgw
Fancy Lighting: https://youtu.be/tl9_LoX082g
New Sprites: https://youtu.be/JMhaMTECy1Y
Corruption Furniture: https://youtu.be/WF1WamNH0ZQ
New Background: https://youtu.be/NkdPo61bSkU

If there ever was a time to buy a new keyboard, that time is coming. This update includes Razer Chroma support. It’s kind of an expensive keyboard, but they keys light up. I found it for about $80-90 on Amazon. I was actually thinking about this some time ago, since I often play in the dark and sometimes it’s hard to see keys when I need to.
https://forums.terraria.org/index.php?threads/razer-chroma-support.57662/

A couple of furniture sets are getting added in, too, including one matching the Corruption.
https://forums.terraria.org/index.php?threads/corruption-1-3-6.58131/
https://forums.terraria.org/index.php?threads/1-3-6-new-furniture-preview.57871/

We’re also getting a new female NPC. For more details check out the wiki and forums.

http://terraria.gamepedia.com/Upcoming_features