I see Kotlin as an alternative to Python, MATLAB, R and other dynamic languages used in the research environments for now. For the iterative modeling/testing process I believe it can show it's more productive than the current alternatives, while at the same time being more performant (relying on native implementations for heavy operations the same way these languages are doing) and being easier to deploy to a real life application.
As for becoming an alternative to C/C++, it may be in some (if not many) cases that the performance loss is justified by the development gain, but a solution to the boxing problem is needed. Valhalla promises to solve this, but it will take a while (which is reasonable, the legacy problem is very complex). In the meantime if Kotlin native is optimised and supports template specialization and value types this could definitely be a C++ alternative, but there is a long way for that.
I propose to focus on the first use case, there's clearly a lot to improve in the existing ecosystem and we can start right away while we wait for the performance problems to get solved.