It seems to me that the interesting angle to this would be to avoid manufacture and instead spend your time on radical CPU designs on FPGA to be made from scratch later. No doubt that doesn't meet the needs of the folks in India.
Obviously, there is no such thing as "complete security" but you can try to secure what you can, that's why people concern themselves with what may seem like unlikely revenues of attack.
I mean depending on how critical your system is, it can really change how you operate. Get a virus on your computer? Some people use anti-virus, and when that says it "removed the virus" they're happy. Other people would only be happy with a complete OS reinstall from a fresh ISO made on a different machine as acceptable. Still other's would require new hardware, it's possible (and has been seen in the wild) to reflash the ROM of the motherboard, or potentially many other low-level chips through software, and to persist the virus through that. Likely no, just depends.