So you would never shift with a bong as Jiu Wan is doing in this photo? Key, for me, is as you stated; "if needed".
No, I wouldn't. It's only "needed" if you do sticky, yielding bong-sau to redirect while attached and the force is too strong. But I think none of that is a good idea anyway.
Not sure what you mean by crossing center and setting oneself up for a trap. Bong and wu as I do them are already on the same side, clearing the path in the same direction >> or <<. Wu is just a continuation of the bong, and laap is done if the punch from the wu hand is intercepted because the bong didn't get rid of the obstacle. By that time, bong has recycled and is now punching with the laap. With two free arms working in rotation, there is no tie-up.