**Apparently I can not post a photo or links since this is my first message on forum.  I will try to post a reply to this message with those links.**

The nearest thing I've found to the instrument I'm asking about seems to be the "B-Cornet No. 4" on an 1894 Shuster catalog page  that I located via a link from this website.

As can be seen in the photo, the instrument is approximately 16 1/2" long excluding the mouthpiece, and has rotary valves. The bell is only about 3 5/8" in diameter. The manufacturer name engraved on the bell is Gebr. Schuster Markneukirchen. I don't seen any serial number or other markings on the instrument.

Would an instrument like this one be only of antiquarian or decorative interest, or do people in vintage bands perhaps still play these types of things?

Looks like your example is in good condition for its age, so chances are there are some players out there who would find good uses for it.  I would assume that it was built to fit the Prussian cornet model of instrument design, with dedicated ensembles in Sweden and that region still using them today.  It definitely has a ridiculously small flare for a German-style instrument, and does seem a bit smaller than the illustration of the No. 4 in the catalog - though who knows how accurate that was.  The unique tone and potential of it being in a different pitch standard than the modern A=440 would make it more difficult to find an ensemble it works well in, but I'm a big fan of bringing underrepresented historical instruments into modern ensembles.