That's a pretty good question. I think I was going for something that looked 'smoky' and naturally fell towards something that looked similar to something I'd already seen. I noticed while drawing and went 'sure, guess that makes sense' and just ran with it.
Sombra's gaseous-looking form reminded me a lot of Parallax from Green Lantern. Parallax was once a member of the Guardians of the Universe and thought he could control the Yellow Power of Fear, and it overwhelmed and turned him into a world-destroying monster. Something like that could have happened to Sombra. Every villain has a reason for turning evil.
I'm glad to know that I wasn't the only one who compared him to Sauron. However, maybe I was asking too much by hoping for a little more direct interaction with the Mane 6.
I'm also thinking that he may be like Agent Smith of The Matrix. His disintegration at the end of the episode is a lot like what happened to Smith when Neo tried to destroy him in the first movie. We all thought he was dead, but he came back in The Matrix: Reloaded stronger than ever. Maybe the same thing will happen here, and he will interact more with the Mane 6 in some fashion.