Speaking of which, guessing the Raspberry Pi 5 with PCIe is going to give the Zimaboard a run for its money.
I even vaguely remember a kernel module (?) that transparently performed in-RAM compression so that you effectively used less memory at the cost of increased CPU usage. Can't find it anymore though.
Zram? https://docs.kernel.org/admin-guide/blockdev/zram.html
It won't ECC your memory, but it can handle compression just fine.
RAM bitflips is one of the sources of bitrot. You may use ZFS, do scrubbing and what not, yet still end up with a corrupted data, because it'd be damaged before it hit the storage.
Google famously ran all of Google search on a million or so cheap desktop-class home-built white boxes (for want of a better term) without dreaming of ECC.
It really depends on the workload and what your goals are. There are plenty of places to introduce bitrot aside from RAM, and it's obvious that ECC can't catch all bitrot.
If you're not checksumming/hashing, then you won't catch it either, and if you are, then the likelihood of the bitrot matching that hash is basically nil and you'll always detect the bitrot.