I don't think that will be good enough.
Looking at all the traces, there is really no separation between 5V and the possibly fatal 120V part. And there's always the odd user that fiddles with the circuit and forgets to unplug the power. I know because I've done that when I thought I was 'in control' and was lucky a few times.
With all the opto couplers it should be possible to move the HV part to a different PCB, box it, and only have safe voltages on the shield. This lacks the coolness factor, but you surely don't want arduino users to end up on the 'darwin awards' list ?