If all you knew was Rust, then getting a job in this already harsh market would be much harder. It would be easier if you knew ML, but it does really depend on what else you bring to the table. So, what else do you know? The job market might change on a dime, make sure you don't just learn the latest hype cycle of frameworks, languages or try to optimize for hiring right now.
I am a backend engineer who have experience building microservices and data pipelines for more than a decade. I felt AI/ML is a natural expansion to my skillset as I currently work on Scala, Apache Spark, Kafka and some Golang.
Yes, then I would go the AI/ML route. I'm also mainly a backend engineer. I considered investing time into Rust as well. But employability is questionable. I'm already in the AI/ML field, so I chose to get more experience in the sales & product side of engineering.
