The idea for a capital ß is pretty old and goes back to the 19th century. One edition of the DDR Duden had a capital ß on its cover. German ID cards only use capital letters and need to distinguish ß and ss. It has nothing to do with millenials.

> goes back to the 19th century

Yes, and so that indicates people are reviving a problem that their great grandparents didn't bother with.

> German ID cards only use capital letters and need to distinguish ß and ss

Are these newly introduced? If not, why hasn't it been a problem so far? If they are newly introduced, why do they only use capital letters?

The 1988 passports had capital letters and used ß as well, not sure what was used before. International standards (namely ICAO Doc 9303, starting in 1980) strongly recommend capital letters but I don't know the reasoning.

The idea is old, yes. But except from the one singular example, noone ever used it. It has no place in the language.

It is not one singular example. Speakers of German have used that letter occasionally for the last 120 years or so and there was a debate to introduce it the whole time.

Show an example of more than ten years ago, please.

Well, one is the first picture in the featured article (it is from 1910). I collected some more here: http://imgur.com/a/NaFgA

And any German passport (at least those issued after 1988, don't know about what was used before).

That can be said about every feature of every language at some point in time.

Sure. Language changes and that is good.

It's not good when an unelected body decides on language changes, without that change already extant and in use by a significant part of the speakers.

This body was (on the German side) put in place by the Kultusministerkonferenz. Their recommendation don't "change" the language (and never could do so). It just says what administration and schools have to use. Everybody else is free to do whatever they want (and many publishers have their own version of the rules).

The changes that were made before (such as the ones in 1996, 1901, or 1876) were made by similar bodies.

This article: https://typography.guru/journal/capital-sharp-s-designs/ (linked from the featured article) shows some designs with corners and stuff. Some of them look less ugly than others. But in all examples except the Backstein one the letter still stands out like an ugly thing that doesn't go well with the rest of the font. More work is needed.