German capital sharp s as alternative

I wanted to do the german capital sharp s as you have instructed in here:

But, I heard many native germans don’t like it or don’t expect this behaviour from a font, so I’d like to include it as an option that could be set on. So default behaviour would substitute germandbls with SS.

So how would you then recommend going about this?

You don’t. This is not the job of the font, but of the text engine of the app that uses it.