KYC stands for Know Your Customer or Client. It's the way businesses go about verifying the identity of a customer/client and to mitigate possible risks, such as illegal/fraudulent activity.
It's fairly controversial when it comes to cryptocurrency, where some form of KYC would actually be warranted, but because of anonymity, decentralization, freedom and a general distrust regarding the storage of said information by a third party, it doesn't happen very much.
In the case of STEEM, it would come in handy to have some form of KYC, in my opinion, to more readily determine ownership of alt accounts, especially ones used for spamming, plagiarizing or other frowned upon to criminal activity.
In my mind, it would be helpful to limit the main account to things like witness voting (even if it is stake weighted), resteeming and maybe even upvoting itself. That action might help to de-incentivize users from making dozens of alt accounts for nefarious reasons to just because.
The likelihood of it happening though will probably take something catastrophic to change the policy and the code to enforce it.