A bit hard, but not crazy. You have to potentially deal with not knowing the mappings, but even random blocks will have obvious marks like Json fragments with "password=", crypto keys with common PEM/DER headers, high entropy 8/16/32-byte data, etc.

I don't think it'd be too hard to find something like private RSA keys in memory, for example.

No it isn't?

I recovered data of mine from ram many times