Thank you for bringing up that question. At first, I personally don't think this will be a technical debt, but rather a natural addition to the current model. In the initial core team's decision, Chris raised a concern:
In SE-0308, we implemented the feature without modifying AST at all. it's only Parser and Syntax change. SE-0308: Postfix '#if' expression by rintaro · Pull Request #35097 · apple/swift · GitHub Before the introduction of libSyntax, we needed to store all #if...#endif information in AST so we can do syntactic coloring etc. even in non-active #if blocks . Now that we have Syntax. Since AST doesn't need to hold syntactic information anymore, adding a use of #if ... #endif is rather simple now. Syntactic tooling like swift-format can support this feature by using the Syntax tree and it'll will probably be an additive change.