Honestly, this chassis will be fine with heat. It is literally drawing air directly from the outside onto both the CPU and GPU. People are getting all worried because there is no other active fans. There is a reason for that - doesn't need them! Most cases have fans to get cool air from the outside to where they are needed - not required here.
That, in my opinion, oversimplifies heat dissipation. Have big or multiple holes and you won't have any heat problems. The parts are still enclosed in a case and heat build-up can happen depending on the parts you have and the use you have of your computer. Since we're limited on the CPU heatsink, once might want to use the L9I. It's a very good heatsink, but it has a flaw. It doesn't send the air everywhere. So if, for example, your southbridge is positioned in such a way that your L9I doesn't blow air on it, the will have a harder time to move away from the heatsink of the southbridge. Granted, for something of the sort to happen, and I'm not specifically pointing to the southbridge as the exclusively being the one stop shop for heat problems, you need something that will generate a lot of heat, say a 7700K and a 1080, and running something that would generate a lot of heat.
But lets face it. Until we get some real benchmark, what I'm saying is speculation that isn't proven, but so is saying the contrary. My point, we need real world testing. But what I do believe could actually be a problem is the overheat of the M.2 SSD. On that, I had done some research last year and found some interesting stuff. For everyone that has a M.2 connector in the back, it's a real possibility in a case this small with so moving air in the back and possibly covered by the PCIe cable. Overheat of the SSD shouldn't make it fail, but what will happen is throttling. You can read on it
here. So even though you might be playing a game or using some software that makes your computer generate a lot of heat and the SSD might be used that much, it could be the opposite for someone else for which the SSD throttling could be a problem. Putting a heatsink on it might help.
I'm not saying this a problem for most of us. I don't think this is gonna be a problem for me. I just don't want people saying it's not gonna be a problem at all when that's not true. It can be in some circumstances. As they say, your mileage may vary.