As someone who uses PHP nearly every working day, this RFC is the first time I've ever seen the ${var} syntax in PHP. It only gets a very brief mention and a single use in an example snippet in the documentation[1]. I don't think I've ever seen it in production code, and would have flagged it as a typo if I found it during code review.

Removing {$var}, on the other hand, would have broken practically every string interpolation I've ever written, and probably about 50% of all uses of string interpolation in the ecosystem.

[1]: https://www.php.net/manual/en/language.types.string.php#lang...