Too many people going into ML could skew the supply/demand into making it a worse job option (more work, less pay), like game programming or academia.
The caveat is that I've worked on ML in the past and I think that the work is maybe less intellectual than software engineering - with complex enough models they become impossible to understand and you start to just try out ideas based on random intuitions. The thing I mostly like about it is the ability to use math and more independent style of work - no scrum, less need for cooperation with other team members etc..
What's happening at least in Australia now is that contract rates (a good indicator of the supply/demand ratio) has halved for ML engineers. Which means (a) a lot of people want to be ML engineers and (b) there aren't that many jobs for them.
It makes finding good positions really hard.