In German Eszett exists in fact only in lowercase. However there is another slot for the capital Eszett (uni1E9E, Latin Capital Letter Sharp S), although I do not know that any use is made of it.
My question, however, concerns the capitalized version.
Since this is an exclusively lowercase letter, it should be replaced with double smallcap S (SS).
For example, EBGaramond contains only the small capital version consisting of two S smallcaps.
Strangely enough, Junicode presents both the version consisting of two smallcap SS, and the design of a small capital Eszett, which it then calls germandbls.sc1; for the latter, however, there is no replacement in the lookups, so I don't understand if the .sc1 extension is just a trick to leave the glyph inside the font without foreseeing any use.
What is the most correct behavior to adopt?