Let me chime in quickly, from the perspective of someone who worked for a few years on Twitter data (see https://scholar.google.com/citations?user=rtKaL18AAAAJ&hl=en...).

The Twitter API used to be extremely open way back in the day. This proved to be a boon for all kinds of social (and not so social) science research. In my mind, this was also one of the reasons for Twitter early growth as it made it trivial to build apps that interact with it. Over the years, the API got increasingly closed, making research in this area extremely difficult.

On the plus side, a decision like this can bring back the good old days of easy access for researchers. The down side, of course, is that it's almost impossible to define "researcher" in a way that prevents Cambridge Analytica like abuses from occurring again (not that the current owner is particularly interested in preventing them)