The idea of simply publishing the private key works only if the private key is definitely not in use anymore. Apart from using forward secrecy for encryption it means that the key was never and will be never allowed to be used for digitally signing something (i.e. proof of authorship, proof of trust relationship...), because otherwise everybody could just take this private key to impersonate someone and claim that the message has been created by the other one before the private key was published.
Also, revocation by publishing the private key means that the owner still has access to the key. This is not necessarily the case if his computer was stolen or compromised by the attacker, but this is definitely a case where the owner wishes to revoke the key.
While one might probably construct a system were guarantees about not signing can be given it looks like your specific system has not this property, since there is actually signing involved to have some web of trust. But in any case it would be better if revocation would be possible without relying on such restrictions in the first place.
One way would not to publish the private key itself but a revocation message which was signed by the private key and can be verified by the public key. This is kind of revocation message could be created at any time, for example immediately after creating a new key. It could also be kept separately from the key and replicated to many places so that in case the private key got lost it would still be possible to revoke it by publishing such revocation message.
And this kind of pre-created revocation message is actually used in practice. To cite from the GPG manual:
After your keypair is created you should immediately generate a revocation certificate for the primary public key using the option --gen-revoke. If you forget your passphrase or if your private key is compromised or lost, this revocation certificate may be published to notify others that the public key should no longer be used.
