This could result in Information overload, especially for newbies. There are already so many threads with useful information for members to read, and I believe only those which contains imperative information should be pinned, like the board description or rules of engagement, such information is not modified often, and if it is, it's structured around the original post and only an edit is required.
but they can be very useful thread that doesn't modify any pin thread, but it has it own space of usefulness that may or should be for everyone especially the late readers
I doubt there are so many of such cases where new threads needs to be pinned and if you do come across one, you could request for it to be pinned. I remember one was recently pinned on one of the boards on request. This is not just as common to be an issue yet.