The important detail to make your theory plausible, and without a huge performance impact and/or jittering, is how the kernel memory management system is going to decide what exactly is those "relatively few pages" on a server that runs a plentiful of processes, many of them including critical/heavy ones such as databases? One such example comes to my mind - transparent huge pages. And it didn't turn out to be quite successful.

I imagine soft-ECC would be more plausible if it could be applied/enabled:

1. Per-process (e.g. whole application)

2. Or fine-grained per-allocation within a process/application

I think both could be implemented through a (system) memory allocator by taking the advantage of page alignment LSBs and/or (non) addressable bits of the virtual memory. Those spare bits in memory can be used to store the encoding of ECC algorithm (Hamming, Reed-Solomon, or something more primitive but less robust).

And then, depending on the ECC algo, one could substantially minimize the performance impact of encode/decode by using SIMD.