I think adding this feature might make posting authors feel like their posts are being replied to by a lot of people replying to their posts, instead of the sadness of clicking and only reading and not replying!
It’s a little unclear what you’re asking for — are you suggesting a way to hide replies to a topic until the viewer has also replied?
Some of the content needs to be replied to by the viewer before it can be seen… well it should be. 
Hi there 
Can you please provide a use case example of what you mean? I don’t understand what you are asking for here? what hidden replies are you referring to?
