That was a very bad suggestion.
I run my NUC with Akasa Newton X chassi which have a far greater cooling area (heatsink) for the CPU and GPU to use (estimated at least 20 times or so larger not counting the folding in the heatsink) than the builtin stuff which the NUCs comes with from Intel. And if I need any extra cooling I can just put a fan close to this Newton X chassi.
And since NUCs are sold by Intel both with chassi and without I would say they really are designed to be used with extra cooling for those who wants/need it (I mean its not like with some laptops where the heatsink could basically be soldered onto the motherboard making it virtually impossible to replace).