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Also someone suggested that all Kotlin Spring extensions should be `inline` for performance reasons (currently only those leveraging reified type parameters are), any thoughts on that?

Usually `inline` needs to be used with careful consideration. It locks you in to your method implementation (you can't change it without forcing people to recompile their code).
Usually it is better to only use it where actually needed (`reified`) or performance critical code using lambdas (like `filter` in the standard library).

The JVM will inline things that should be inlined, usually.