For what it's worth, I'm currently implementing the Binary AST parser (using the current candidate AST) in SpiderMonkey (which uses its own AST, of course) and

For what it's worth, I'm currently implementing the Binary AST parser (using the current candidate AST) in SpiderMonkey (which uses its own AST, of course) and that doesn't cause any issue so far. The AST used in the file is a convenient abstraction but doesn't need to match the AST used in-memory.