While this is a very great idea, I believe every one has this in mind already with the advent of steemmonsters and SMT which seems like a prefect pre-cursor to such an idea.
It would have probably been the next main feature after SMT. All the same, here is my humble opinion further suggesting that this idea should be integrated as a sub feature under SMT , this will definitely be after the SMT-LITE goes live.
My Suggestion
I suggest that you rewrite that proposal in such a way that it easily integrates into SMT in which a coin issuer can decide to choose between issuing fungible or non-fungible tokens at the point of issue.
When he does create fungible tokens, the steem blockchain adds an extra editable json field to all the soft data of spendable units of tokens.
This field can be edited only by the issuer and still remain editable by the issuer even after it has been issued secondarily to new spenders.
This means through out the life of that token , the issuer has a right to edit it, maybe the issuer will be given some sort of privileged keys to do this and nothing else.
This way, issuer can always trace its tokens and edit no matter who he re-issues or send it to. Maybe there will be a kind of api command that allows issuer to have a list of all its tokens no matter who claims ownership.
For Instance:
An issuer can decide to programmatically edit his token extra json field to contain different kind of dogs with different kind of behaviour through some looping system that generates random data like how most crypto-game collectibles are made. Over time, he can change the parameters of this json data depending on how the game the token is based on works.
So, that is the idea but due to constraints on time and human resources on the side Steemit Inc, I really don't think this can be done now.
All the same, trading this tokens will need a sort of integration when trading with other non-fungible tokens.