Proliferate was a big deal back in New Phyrexia, since you can add poison counters to players with each proliferate trigger. There are plenty of Infect creatures from the Scars of Mirrodin block in White, Blue, Green, and Black. So, you can see the appeal of having all 4 colors at your disposal. But as someone who has never been a huge fan of Infect as a win condition, I'd like to find ways to utilize her a bit less one-dimensionally.
What's most awesome about Atraxa is the sheer number of abilities on her. Not only she is a 4/4 flyer for 4 mana, but she also has vigilance, lifelink, and deathtouch. There are so many dimensions to build off of here that a single article can't possibly contain all of the potential builds!
Personally, I'd build a Voltron style deck with Atraxa that utilizes Auras and Equipments which offer +1/+1 counters, such as the Ordeal Cycle from Theros. Then, I would also include other ways to proliferate such as Contagion Engine. Atraxa is always going to be a ton of fun to play with, even if some of the more obvious themes are built around her for the most part.