I remember you said exactly this in HardForum when someone tried to put a 120mm AIO inside Sentry back in the days of 1.1 and you ended up supporting it in Sentry 2.0. ?
This is a bit different though.
Quite a few people asked about getting rid of internal SFX PSU in order to fit AIO or just figuring out a way to squeeze in the AIO while still having the full sized GPU. The 120 mm AIO made sense at that point in time when R9 Nano came out because it seemed like we might be getting a fairly standard form factor of ITX-sized GPUs with reasonable amount of performance (R9 Nano/970 Mini/1080 Mini/2070 Mini etc).
And it made a lot of sense in quad core/8 thread i7 generation as it actually let you make a virtually silent/really quiet gaming rig laying in front of TV because the 120 mm AIO could keep the 65W TDP CPU at really low temperatures at the same time helping vent the back of the GPU compartment.
The issue with 120 mm AIO right now is that most of the potential users of such case want to use full length cards because the power draw went up for both GPU and CPU and thus the ITX sized cards will be only made for the lower end chips and at the same time it doesn't make really that much sense with current gen CPUs as it did with 65W quad core i7 three years ago.
We have missed the mark on that because low profile/slim 120 mm AIO kits were made end-of-life right around the moment we were already preparing review samples batch to be sent to youtubers. And also we didn't knew that Zen2 will change that much when it comes to thermals. Second issue is that, while every significant 120 mm AIO had long enough tubes to route them neatly inside, we missed that the Corsair H55 had slightly shorter tubes, and most of the youtubers did build with that which came out terribly. So that's also something that affected how many people were interested in making an AIO build.
At the point of designing this feature, it seemed like a potential mainstream configuration or one of mainstream configs, but after the reviews and feature videos, there were simply no interest. So its not like we made support for something just because a few people asked for it, it made sense to have it at the time of design, but since the whole process takes time, we were late with it.
Also there was barely any cost involved in supporting the 120 mm AIO within the perforation, but for things like making access panel to the back of the board, making mount for the AIO in place of PSU and then additional mount for HD-Plex somewhere, making holes somewhere to route the liquid cooling out of the case - it was always going to over-complicate things and make the case more expensive for everyone. In case of having quick connects - iirc, those have pretty big diameter so figuring out where to place them would be pretty hard unless there was something like a cut-out where the power connector at the back is and so you would have a swapped piece similarly to like Sliger does it for taller GPUs. But this would mean two additional pieces, a method to mount them and reinforcing the case structure there.
Why? Maybe somebody loves your unique design enough to want it on top of their desk, but have the needs and the wants to place the radiator somewhere else, and thus make the build completely and absolutely silent.
Well, this makes sense on its own, but once again - how many of you are actually going to do it this way? I'm kind of against making contraptions like this, or for example making ultra small cases that require huge brick to power up the GPU unless the whole point is to make it split for transport. That's my bias though ;p