If Stella and Adam do have a thing, maybe it will make Mac realize how he feels about Stella, or maybe we'll get to see a Jealous!Mac.
I saw a scene from the first episode where Mac is talking about how he feels about the case, how frustrated and angry he is, and I love how Stella says 'You're not alone in this, Mac' - both calling him out, gently, on being so intense about the case and talking about it as if he's the only one affected, and also offering her support. Mac can be both self-absorbed at times, and also he tends to feel responsible for things he can do nothing about (like Danny being in a wheelchair) and I LOVE how Stella calls him on such things. He needs that. I hope if something does happen with her and Adam, say a fling which she later regrets, Mac will be there to do the same thing for her - call her on her behaviour, but support her too.
Of course, if the 'complicated, difficult' relationship Melina mentioned is Stella/Mac....that would be very, very interesting. I can see them turning to each other for comfort in the aftermath of the shooting, especially since I think they both feel responsible for taking care of the others.
I'd love to see Mac and Stella go into Kick-Ass mode to track down whoever is responsible for the shooting, they're awesome when they work together. And Mac will need someone there to stop him going over the edge - he seemed very intense and stressed out in that scene.
Also, seeing them come together to support Flack, Danny, Lindsay and Hawkes as they all face the various problems mentioned in the spoiler thread, and deal with the aftermath of the shooting, would be great to see.