PhD means %u2018Doctors of Philosophy%u2019. It simply not about a degree but validating an individual%u2019s intellectual capability which simply means ability to fathom, analyse, validate, execute and revalidate about virtually any subject. So it is just not about an individual's competence in his chosen field but his very intellectual capability which founding fathers felt will only increase with experience and worldly wisdom. There may be fake PhDs but simply suggesting to periodical revalidation of PhD means, to put simply, expressing ones ignorance. What we need in PhD is not subject after certain level of intellectual capability - but 'philosophical' aptitude. It is better, the author first understand the true meaning of word 'philosophy' as enunciated by greats like Radhakrishnan, Vivekananda, Socrates, Aristotle.
That would probably answers whole stuff. It is about %u2018spirit%u2019 of degree not %u2018letter%u2019 of it. If you devise a system that validates the 'spirit' than 'letter' then we can welcome. But that validation is already there is system, we just lost it in our quest of material pursuits.