Right off the bat, let me say I'm not a developer, so I'm not sure about the possibility of this feature on the Hive blockchain.
But if it is possible, it would open up Hive to a new audience - literally. Everyone must me familiar with the guest comment feature on mainstream blogs.
Suppose you come across a blog that stirs you to interact - you might want to troll them, appreciate them or question them but you don't have an account on that platform so you have the option to leave a comment as a guest.
Another reason could be that you wish to remain anonymous, this may not always be due to ulterior motives and cowardice, it could just stem from restrictions on individuals due to their employers.
More visibility?
A lot of initiatives use twitter, reddit and other traditional platforms to market their content. As a twitter user I always think that even though I'm tweeting this, would my followers interact with the blog? With the guest comment feature it will help non hivers comment and possibly increase interest about the decentralised social media.
But why wouldn't people just signup?
There are so many people who wouldn't bother to sign up just for the sake of a single comment. Although the signup process has become faster, a user would need to understand the HIVE blockchain which has a certain level of time investment.
But the only problem is...
Spam wham thank you ma'am. Anonymity encourages trolls and spammers, which could end up being a huge concern.
But I still think the benefit outweighs the drawbacks.