I see no reason to get "mono-blocks" if you're doing class D as literally the only difference is two power cords vs. one. I suppose that's another opportunity to waste $300-$1000 x 2 on expensive "directional" power cables, but it'd be a total waste.
Depends on the amplifier. To be a true dual mono, requires splitting of the power supplies at the incoming AC power. If you share a power supply there is increased capacity for crosstalk, which is readily visible in crosstalk measurements (which I guess Stereophile no longer will do). Lots of the ICEpower modules for instance com in powered (AS) and non powered (A) so you can create whatever kind of amplifier you wish.
Not all Class-D have dual power supplies, so therefore, yes, there is some difference possible.
Can you hear it? I don't know. :)
But it's more than just about power cords.
Best,
E