Let’s be honest though. I don’t think anyone really believes that the toString implementation for data classes will change in the near future.
I haven’t seen any discussion about changing anything there and I can’t come up with any argument why you would want to. So unless you need a 100% guarantee that your implementation will work with every kotlin version for the next 10,000 years toString should be fine.
Otherwise I suggest you override toString yourself just to be sure. Also I guess you can use an annotation processor to generate you a function that generates the string if writing it manually is to much work but this is an extreme solution.