[teruakohatu]

But why remove it in the first place. Is it such a burden on the parser or mental overhead for developers?

[sam_goody]

Because this syntax is used for variable variables as well as interpolation.

By removing the interpolation, it makes the remaining code more predictable and less likely to have a footgun.

[the_mitsuhiko]

> clears the ground for adding any-expression interpolation, which PHP is currently missing