Simple RAW 3

[PhoenixPhyre]

If i may, couldn't be argue that if the spell (just like Scorching Ray and other spell like this) targets only one creature (even if it could target more), then it could be twinned.

At least, i think this is a possible interpretation.

That's explicitly precluded. If, at the level it's cast at, it has the option of hitting more than one target it cannot be twinned (at that level).

To be eligible, a spell must be incapable of targeting more than one creature at the spell's current level. For example, magic missile and scorching ray aren't eligible, but ray of frost and chromatic orb are.