This statement is false. The limitation of a class D amp is similar to what is is with any amp- how big are the heatsinks, how much current can the output devices handle, and how much current is available from the power supply.
This statement is just by someone protecting their yet to be released Class-D. If you say then put big heatsinks and power supplies on it if you want them to be able to drive the many hi-end speakers with low bass impedance combined with large amounts of - phase shift. (smoke screen, using small form factor as the excuse)
Lets see if the yet to be released class-D amp can truly double from 8 to 4 to 2ohms, without understating as many now do the 8ohm to make the 4 and 2 look good, thank god for Stereophile pulling them up (but quietly) on this understating 8ohm wattage practice
Everyone knows that Class-D can’t do the wattage doubling act below 4ohms, it’s shown in every "legit independent test review", mostly by not even giving! the 2ohm figures.
And certainly not like the better complimentary bi-polar linear amps can, when driving speakers that have hard loads, like the Wilson Alexia etc.