Wouldn't that add a transactional cost to bitcoin, not unlike PayPal or Visa?
Honestly, the best thing for the bitcoin ecosystem is to learn from Paypal and Visa, and to emulate their good qualities. I know it's popular to hate on the existing ways of doing things, but the existing ways have a lot of hidden wisdom embedded in them.
This could lower the transactional-risk cost between doing business with certified exchanges, and still allow users to do business outside but with the increased transactional costs.
But then again you're just building another financial exchange system controlled by the certificate issuer - except it would need to be backed by some form of international enforcement (e.g. WTO?).
Where is the benefit to bitcoins then?
You won't need insurance when the coins simply can't be stolen.
It'd be a good idea for Coinbase to implement, though.
But there are also some online wallets that already implemented it:
https://www.bitalo.com/ (this one is also at the same time something like localbitcoins.com)