What would the consequences be if I did (whatever the other person just mentioned)? Implies that the speaker either believes they are right to do something, or else they are suspicious of the other person questioning them about it. A: "Your team isn't actually going to present that plan to the board, are you?" B: "Suppose we do? It may be a little unconventional, but they'll see that we are right." A: "So, what, you're going to just hop on a plane to Europe and show up on her front door?" B: "Suppose I do? I've always wanted to go to Europe, and at least then I'll know for sure how she feels."