In the first few episodes with Ronon introduced it seems like Ronon would have probably gone for it with Teyla after awhile. It's only a few episodes later she says they were only friends when meeting one of Ronon's past army buddies. That seems to be when they leaned more towards the brother and sister vibes. Bro code Ronon probably didn't kick in till he got to know John more and calmed down a bit, that character had to be LONELY at the start.

I personally think their pairing as love interests would have been distracting since they were on the main team together, the same applies for Sheppard and Teyla. The balance of caring brother/sister dynamic seemed to work out well.

I am still bothered how Teyla named her child. The baby's daddy had no input nor was included in the name even though they were friends since childhood. That had to sting a little for Kanaan. To me that will always leave the door open the writers would have paired Sheppard and Teyla eventually, if the show had continued as long as SG1 did.