Low power-factor loads could certainly result in phase shifts leading to a higher neutral current. With, say, a 60-degree leading phase shift on one phase and 60-degree lagging on another, the currents would then be directly in phase and add in the neutral.
Obviously even at higher power factors the result could be more than 16A in the neutral with two 16A loads.
Whether such a situation is likely to occur in normal usage is debatable, but it's certainly possible.
And no, the RCD would not trip on an open neutral, because the currents flowing in the phases would still be balanced overall.
