Well, I agree that Sten doesn't look like a guy to joke around, but he's good bud. Also, I don't think it's considered "fatal", because how the crap they would reproduce? It may be... Painful... But... Eh... Sounds fun! That's why a Qunari romance would be interesting.
We had a Turian romance on Mass Effect 2 and, hell, I freakin' want a Krogan romance on Mass Effect 3, so DA2 MUST have a Qunari romance or I'll go 'bear-serk' (Persona 4 joke).