Depends what you mean by mass exodus. I think there is certainly an unprecendeted number of people leaving JWs at the moment, for a number of reasons, and there are indications it will continue to get worse. Does that count as a mass exodus?
1. Most western countries are now flat or declining. This has not happened since the fallout after 1975 and in that case it only lasted a couple of years. This is a much deeper and enduring trend.
2. shepherdless has demonstrated that JWs are getting older. This change has occurred over the last 10 to 20 years and is highly significant because increasing age profiles of religions are invariably followed by declines in adherents. And the speed and extent of JW aging population is pretty dramatic, even when compared with data for such steeply declining religions as Methodism and Anglicanism in the UK. From having millions of adherents in 1950, on current trends there will be no Methodists left in the UK by 2050. In fact probably sooner than that. (I think 2033 was the estimate one sociologist gave)
3. It is harder than ever for JWs to actually believe JW teachings: 1914 is over a hundred years ago, overlapping generation makes no sense, the faithful slave teaching is changing and looks self serving and increasingly neurotic. And this comes at a time when all these issues, and others, are readily exposed online in many formats. JWs may have a talent for believing unlikely things, but even they may increasingly struggle with the burden of absurdities. Young people in particular.
4. Society itself is becoming increasingly secular and liberal. And it is becoming increasingly difficult for young JWs to maintain positions such as creationism and opposition to LGBT equality, in the face of evidence and prevailing opinion. Most don't think it's worth the bother and so most young JWs now leave the region.
5. Plus you've got the thousands of JWs who have been removed from bethel or special pioneers who have had monetary support removed.
Those are just a few factors. There are many more that indicate JWs are reaching a tipping point. The fact is that their growth is already the poorest it's been since 1975 and there are mulple indications it is going to get a whole lot worse. Does that count as a mass exodus?