Syntax trivia is a very important component and a pretty natural fit once you start thinking about the feature that we decided was absolutely necessary: full-fidelity round-tripping between parsed syntax trees and the original source.

I think this is one of the most common mistakes compiler writers make -- they don't spend enough time thinking about incorrect code. Let me be clear: most code is wrong. If your code is right, you compile it once. If your code is wrong, you compile it many times until you get it right. More importantly, if you run your IDE off your compiler, almost every character you type is a wrong program.

Having a full-fidelity syntax tree is essential for having great experiences with wrong code. In addition, it easily solves the problem of having to serialize your trees -- the source text is the serialization.

This feeds into API considerations as well. A number of people have repeatedly talked about how cool it would be to have a lot of other tools understand your AST (like if Git could support checking in ASTs instead of source). This is the wrong way of looking at it. If you're dealing with a raw AST you often have to have domain-specific knowledge of the language itself. Instead, what you want is to take the thing with the most domain specific knowledge, the compiler, and allow it to answer questions, i.e. have an API. By having round-trippable source, all source is essentially given a transparent API that can be used just as if you were interacting with the source code itself.

Anyway, this is going off the rails, but it's one of the numerous things I'd point to for many production compilers and say, "you are the past, this is the future."