I noticed this completely by accident today (not sure if it's been addressed anywhere else) and thought I'd bring it to people's attention.
You are now able to @reply Viners and have them receive a notification for doing so, something that previously didn't work if you simply typed it out.
To do so is pretty simple. You just type the "@" sign and a dialog box opens up for you to type in the username of the Viner whose attention you'd like to call out.
This is especially useful if you need to get somebody's attention in a battle thread.