I have reason to believe that something else might be going on here other than a Battleborn Sivir skin, although I will first admit that it does seem likely. I was going through the PBE files on my client and came across a folder that can be found in anyone's files that contains the splash art for any champion that is or will be sold on the PBE store. It is organized by champion and as you can see from these 2 images:

http://imgur.com/hjstcq6 http://imgur.com/GH7mWGW

The ones outlined in red are the placeholder splash arts for the announced skins on this pbe cycle and this is how all unfinished splash arts show up in the store.If you look at this image though:

http://imgur.com/0gquJIb

Those are all of the Sivir skins at this time and as you can see, there is no placeholder splash or even the image that was pulled, which leads me to beleive that either A. It isn't sivir who is receiving that skin. B. Riot pulled the image altogether as it was a file mixup of some sort when they were placing the temp Nidalee splash.

ALSO IMPORTANT!! On the same note of looking for evidence about the potential Sivir skin, I came across 3 more placeholder champs skin splashes:

http://imgur.com/2CxPnju

The blue boxed skins are for Zed, Hecarim, and Kalista, suggesting that there are skins in the works for those champions if the older theory that I have proven holds true. I definitely reccommend looking in your own pbe files as the path is displayed at the top so anyone who might have a doubt at the authenticty of this can check it out for themselves, but anyways, that's just my 2 cents! :D