I would be happy with SATA SSDs in the 12-20TB range for my Synology NAS. Sure, the interface of a single drive limits bandwidth, but SHR addresses that; my current 16xx with 6x 16TB mechanical drives can cope with a 10Gb LAN connection and manage almost-wire speed transfers consistently. Replacing the HDs with SSDs would easily accomodate 10Gbe transfers, possible bi-directional, or even 2 x 10Gbe interfaces.
Of course NVMe is faster, but the largest NVMe drive I can find is 8TB and horrendously expensive. And no doubt hot. Give me a lower-cost SATA SSD, with a memory technology that can handle SATA-III speed (or close to it) and I'm a happy bunny with a RAID
I like the Synology [other brands available] form factor and low power draw; I dont want to build a tower with an EATX board to handle multiple PCIe-attached 4TB NVME drives (I would need 5 PCIe adaptors and 20 drives just to approach 80TB).
But hey, I was also hoping for a single-slot PCIe graphics card in the days of the 1070. Its taken until the 3050 for it to become reality.
In regards to backups, I agree with that best practice dictates backing-up to a different media, but what consumer media has the capacity, interface, and the right price point? As it is, I backup key data, not the entire NAS.