>Any kind of writing system allows this.

The meaning of the words will change over time, but not the words themselves. So someone who reads it will know what the words written actually were, and just have to lookup any differences in meeting between when the words were written and now.

Imagine for a second if we took Shakespeare and rewrote it with modern day English, and then made the claim the new version is the original Shakespeare... I think we would see the problem with that. But that is what happened with emoji. It isn't that people look back, see as collections of pixels, and realize now those pixels mean water gun while in the past they meant firearm. When they look back, they see water gun.