Has there ever been a trend in academia like the one we're experiencing with Data Science?
Does any field in the past compare to the current field of Data Science, in terms of trendiness and importance?

Yes. It has happened before, it is happening now, and will again.  There was programming in the 80's and 90's.  Then Software Engineering... 
Back in the late 40's and 50's there was a big boom in nuclear physics, and nuclear engineering.

Don't get a degree because you think that there might be good jobs.  Do what is interesting to you (and something that is likely to get you a job.)  If you like Data Science, then do it.  If you don't, then don't.  you are going to have to live with doing the work all day, every day for many, many years to get a PhD.  If you aren't in love with it, then you will not succeed.   

Since a PhD is a long-term commitment, takes a lot of patience, costs a lot of money and takes a lot of time during the term, it is not to be undertaken by an answer on the internet. It is your decision.