Now we can start talking about overkill for Openhab.
8GB Ram and NVMe 
Looks nice! I like the form factor and the new 100-pin connector - but no perfomance boost over the RPi4b (besides the separate Gigabit-LAN Chip). eMMC-storage is nice but isn´t much more robust than SD-cards AFAIK.
And it´s a bit funny, that theres a separate PCIe1x slot now, but booting from an attached NVMe isn´t possible yet. 
So, theres no obvious reason (certainly not for OpenHAB) to upgrade from a RPi4b (2GB) to a CM, besides the hobbyist-factor of building your own hardware.
So, as you already said, total overkill. But I know me, so I will order one soon… 
Great. Now all I need to switch my lights even faster is a matching enclosure… SCNR.
With an extender you don’t have to worry that much about the enclosure. Turning on/off lights faster right around the corner 
Try searching for raspberry pi nvme expansion board. I don’t own one myself, I run a regular ssd via the usb3 port. You really don’t need a ssd drive for OH, just buy a durable large sd card and use together with zram.