Regarding Julia 2.0, there is no real concrete plan for that to happen any time soon and there is plenty of non-breaking work to do before then. Within Julia 1.x, Julia is committed to backwards compatability, although there have been some known exceptions. For example, the default dynamic task scheduler is potentially an issue for old code. Packages such as Compat.jl also help with forwards compatability.
Don’t take my word for it. Here’s Stephan Karpinski on the topic.
Also above that post you can see Matt Bauman saying note to take too much from the 2.0 milestone marking in Github.
Julia might have an easier time at maintaining backwards compatability than Rust since generally Julia source code is the primary form that is distributed.