You have my attention. Well, this plus that 2 x 3.5 inch bracket you mentioned on [H]. What sort of limitations would these introduce?
Well, unfortunately, the dual hard drive cage has been nixed. After designing it out, it became far too complicated to produce. Plus, it takes up the spot of the bottom 240mm radiator. So, if you planned on using the ATX PSU bracket (which takes up the spot of the front 240mm radiator), you'd be left with one 240mm radiator for all of your parts. Not the best solution.
The ATX PSU mount attaches to the front 240mm radiator location. Because of the limited space from the front of the case to the motherboard tray, you cannot mount ANYTHING else on that radiator mount. My case is so narrow that it fits a normal size ATX PSU width wise, but only with about 16mm left of space. Length wise, the PSU will touch the end of 10.5in cards. If you go with the PSU mount, you'll have to get VERY creative with tubing runs and pump/reservoir placement. Also, you'll have to limit the card length to 10.5in when purchasing components. Won't be an issue for cards such as the GTX 980/Ti, Titan/X or R9 290/X/390/Fury/X but some cards may not fit.
About the hard drives: with SSDs becoming larger and larger, and also cheaper, I fail to see the need for 3.5in drives. This is my personal opinion on that matter and I realize it may vary from person to person. However, with that idea in mind, that's why I never intended to be able to mount 3.5in drives anywhere in my case. In hindsight, I could have widened the case a little more so you could fit 3.5in drives underneath the motherboard. However, to do that now would cost me several hundred dollars on a new prototype and take more time so I am trying to find simpler solutions to the few existing problems.
-Jeffinslaw