From my read of this, they are basically going from being a complete searchable reddit archive for researchers (and anyone else) to being a archive for the use of Reddit moderators only, and then only for the subreddit they moderate.

Which, assuming Reddit isn't paying them, seems pretty much like "We have decided to allow you to do a bunch of unpaid labor for our profit-making benefit as long as it's not useful to anyone else". No idea what they're getting out of it.