If we required something like a P.Eng, which (at least theoretically) means you are responsible with real consequences (for say bad building design) then certified employees will be far more reluctant to attach their name to shoddy practices. This bubbles up to the employer. If a client requires you to have certified P.Eng sign off then there’s some reassurance it’s not just going to fall a part.
I don’t think you need this for everything in a stack, but security wise it might be a good idea.
The problem there is that everything on the stack is a potential hole. The chain is only as strong as its weakest link.
We accept that possibility in SaaS though... for now.
Most successful SaaS applications probably weigh in at 250k LOC or more (I know LOC isn't a great metric, but it serves as an idea of an application's complexity) and will use many libraries that themselves could be questionable. Seems like it would be pretty complicated to certify.
People without credentials but with experience and care can produce a reasonably secure system. People with credentials but under time pressure and contradictory requirements, and willingness to cut corners, can produce an unsafe system.
It's the system that fails. It can be inspected the way buildings are inspected.