This is good news. The dart language has been getting more complicated without corresponding quality of life improvements. A first class record object without messing around with macros would be a great start.
In practice in a Dart app you usually use freezed or something similar: https://pub.dev/packages/freezed
i.e. I annotate my models with @freezed, which also affords you config of the N different things people differ on with json (are fields snake case? camel case? pascal case?) and if a new N+1 became critical, I could hack it in myself in 2-4 hours.
I'm interested to see how this'd integrate with the language while affording the same functionality. Or maybe that's the point: it won't, but you can always continue using the 3rd party libraries. But now it's built into the language, so it is easier to get from 0 to 1.
When the language implementors start making larger programs, it will soon become apparent how the program organization is hampered without named, defined data structures.
I didn't add structs to TXR Lisp until August 2015, a full six years from the start of the project. I don't remember it being all that much fun, except when I changed my mind about single inheritance and went multiple. The first commit for that was in December 2019.
Another fun thing was inventing a macro system for defstruct, allowing new kinds of clauses to be written that can be used inside defstruct. Then using them to write a delegation mechanism in the form of :delegate and :mass-delegate clauses, whereby you can declare individual methods, or a swath of them, to delegate through another object.