The Risk of RISC-V: What's Going on at SiFive?

I don't think it's so much "security by obscurity" as it's an issue of a much lower bar for chip production. Intentional back doors or malware represent a huge risk for a product line, so manufacturers won't put them in without someone like the NSA leaning on them. It's a simple risk/benefit calculation.

But the risk is much lower if you can snag a processor design off the 'net, make your modifications, send it off to a fab and sell it under a fly-by-night operation. If it's ever discovered, you take the money and run.