Wouldn't it be cheaper to just build any NAS and chuck Debian on it if you didn't care about the OS and vendor software to begin with?
In theory, one could fit an Arm RK3588 SBC with NVME-to-PCIe-to-HBA or NVME-to-SATA into half-depth JBOD case. That would give up 2x10G SFP, 2xNVME and ECC RAM.
As I understand, migrating to other hardware wouldn't be an issue if availability becomes an issue.
The Marvell CN913x SoC has been shipping for 5 years, following the predecessor Armada SoC family released 10 years ago and used in multiple consumer NAS products, https://linuxgizmos.com/marvell-lifts-curtain-on-popular-nas.... Mainline Linux support for this SoC has benefited from years of contributions, while Marvell made incremental hardware improvements without losing previous Linux support.