This is kind of a w3c Verified Credential (VC) but stored into a blockchain?
After read the VC spec, I found (maybe im wrong) that the way you are aiming to dealing with the revoked certificates its indeed more decentralized and reliable than the used in the current VC spec (its relies on issuers servers, if got it right). And with the use of IDDs I see a certification system that do not relies on issuers servers at all.
Yes
Sort of, only the hash of the document and the potential merkle root (batch issuance) are stored on the blockchain, not the document itself.
not quite, we are following the BitstringStatusList spec as (candidate) recommended by the w3c, so in practice the hosting the status list credential may or may not be decentralized, depending on the issuer’s strategy (document only has to be retrievable, but it could be webhosted or retrievable behind an API that handles decentralization).
Again Blockcerts does not go as far as to prescript the way documents are hosted and shared. Any issuer can come up with their own way of managing the documents.