Kalista won't be getting a new skin until Riot decide how to change her to make her balanced. As her kit is right now, in order to be good in lower levels of play, she has to be 100% of the time pick or ban in pro play. In order to be balanced in pro play, she has to be 30% win rate in lower tiers. While Riot will typically balance to the higher levels of play, they also want champions to be playable both in high and low tiers without being too overbearing or underwhelming in one or the other. A big thing about Kalista that causes this need is her team reliance. She is highly reliant on a single teammate, her support, as she straight up doesn't have an ultimate if that player leaves her. However, her other issues include that she has just too much stuff: dashes on every auto, an execute that can kill dragon/baron earlier than Nunu, her ultimate is an insanely powerful engage, and she has a free vision tool. As such, Riot doesn't want to influence people to play her by making new skins for her.