Any sort of legal action will require a VERY high bar to have any chance of success.
Its not really a safety issue so unlikely to fall under recall category and get NHTSA involvement.
Any failures that are outside of warranty already face an uphill battle.
Because of the effect of OCI, you're going to need full maintenance records.
Realistically, you need sort of evidence that Subaru was aware of the problem, and did nothing to address it. Subaru did try to address the issue by switching turbos, and lowering the OCI for 08-09.