He's still not convinced this won't fizzle out before they put it into practice or that it'll go up in flames if they get far enough to get the bands in order, but this is a start. They should at least give it an honest try, shouldn't they? Seems such a waste to do anything else.
"You don't think so? I mean, you haven't thought of it?"
He's a little surprised at that, to be honest, and maybe it's because he's such a creature of emotion that this part is easy for him. He's always relied on gut feeling and big, grand, romantic gestures. It's something he's confident in and realizing that neither Jack nor Ianto are quite as sure of themselves is... weird. Comforting, but weird. At least he got this part mostly covered, even if it is a tangled mess.