Well, you could come up with something recognizable for the fun of it, but it would only be of any use when setting (or writing???) all-caps cursive, which is a monstrosity.

Right; I was more interested in what it would look like and didn't really think it through.

A hypo-theoretical italic small cap “Eszett” ß would however mimic a hypo-theoretical italic cap Eszett. Some people here in the forum expressed that they wouldn't buy a font without italic small caps, as google reveales.
But if German language users would mind if an italic small caps Eszett is “missing”? Put into context, italic small caps would be necessary for acronyms maybe. As of 2011 I think it would be an exotic glyph, and the idea is already two steps ahead of the current use, as the people who even heard of the Eszett cap in the first place are few, but why not being two steps ahead?

Offhand, I don't recall any types with cursive (joined) capitals.
But if we're talking about discrete swash capitals, first, you have to have a typeface where the swash caps have been designed for all-cap setting, not just as initials.
I've done a few such types: FF Oneleigh Pro, Scotch Modern, and FF Fontesque Pro (top to bottom)—

For Oneleigh, I was able to come up with a unique swash form for the cap eszett, but didn't think it would be merited for the more demure swash caps of the Scotch Modern, where the default Eszett already had the ball terminal which is the primary feature of the swash caps. In Fontesque, the default caps are somewhat swashy—I suppose I could have come up with something special for the cap eszett, but found it easier to adapt the Oneleigh Italic glyph.

I haven't produced swash small caps for any faces.

I am sorry, I mixed up italics and cursive.

Thank you, everyone, for your input, even if the question was a bit odd to start with. I originally asked the question with a Spencerian script in mind; I didn't bother to ask myself why one would use such a character. But the all-caps swash styles are fairly close to what I had in mind, and certainly more practical.

You can start from here:
http://typophile.com/node/33647?page=5#comment-430065