For the record I think Rust has a lot going for it, but it is not the C++ killer that many are touting it to be.
That said, there are many performance-critical applications who are not security-critical, and in those I'd expect C/C++ to persist pretty much indefinitely. And many security-critical applications which are not performance-critical, and can perfectly well be served by garbage collected languages like Java/C#/Go.
To modify this I'd say that becoming reasonably good is pretty easy (and I'd agree easier than skiing). To be become really good takes a long time and a lot of dedication and the difference in difficulty between skiing and snowboarding disappears. Same as with programming, some languages make it easier to go from 0 to your first app, some make it easier to write solid production ready code that earns you a paycheck, but becoming really good is always hard and independent of the language you're using.
I don't know how people can be so sure of this. We know essentially nothing about how to teach or learn Rust effectively, it's something that the community is just starting to look at. However, one thing we do know is that the detailed support that the Rust compiler provides to the novice programmer is quite simply unparalleled in other mainstream languages. It's basically the ultimate T.A.
