I have a Supermicro 826 myself (SC826E16-R1200LPB being the exact model) which I have heavily modified: different backplane, different PSU, different fans, and adding a 2.5" SAS/SATA drive cage at the back (MCP-220–82609–0N) plus the respective rear window (MCP-240–82608–0N).
So when I read this article, I, like many others it seems, was intrigued by the NVMe drive cage at the back of the chassis, thinking about replacing my SAS/SATA one with it as I actually have a two Intel DC P3700s 1.6TB installed in my server. But besides the fact that it seems impossible to find over here, I thought about one aspect that tends to be overlooked when it comes to enterprise NVMe SSDs: they actually draw quite a bit of power and need proper cooling.
So unless you have truly excellent cooling (and hence, very high noise levels with just 3 x 80mm fans installed in the 826), putting two drives which consume more than 20W each (when writing data) in a small drive cage at the back of the chassis that hardly gets any airflow unless your chassis fans run at Ferrari-like RPMs (definitely not in my case) is probably not such a good idea.
I have an ATX board installed, the same Supermicro X11SPH-nCTF, and hence have quite a bit of space on the side of the board right next to the fans. As I have no intention to replace the brandnew board with an E-ATX one anytime soon, I used some double-sided tape to 'install' my DC P3700s there, connected to the OCULink ports of the board.
I know, I know, you're thinking 'how Ghetto'! But it actually works fine, both drives are properly cooled despite my slowed down fans and I don't really need them to be truly 'hot-plug' anyway, as they are used as redundant cache drives. Really love the Intel DC P3700s btw., ridiculously fast drives.