I'm interested in building my own frame one day, but for now, while I practice brazing, I'm just looking at design elements and trying to figure out what I want in a frame.
On that note, I've seen a few bikes (though not many) with wishbone seatstays. This feature is more common with new bikes in carbon, or with carbon elements, but I really like the look on a steel frame.
Are there unique and desirable ride characteristics offered by a wishbone seatstay, or is it more flash than substance?
I don't really find them attractive, but I respect the fact that other people do. I suspect they add quite a bit of weight and (undesirable) stiffness depending on how they are done. I have a wishbone fitting that is a lot like a fork crown. Not sure what blades were supposed to go with it, the blade sockets are fairly large.
I'm not sure it is called the same thing, but it was comon on MTBs in the 80's? Nishiki did a lot of them. They have the advantage for certain bikes to allow stays (top or bottom) to be unlimited in length. They also look easier to fit it reducing the fit to a bunch of end on butts, that can be cut on a mill or straight from a miter program, or are square. Something like th Strawberry casting does look heavy to me, but I have not handled one.
As far as reducing the difficulty of making the joint at the seat, you can use Bontraged stays which are a slip fit (5/8" .058" wall over 1/2") (allows the stay to extend like an antenna) to allow you to work up to either end without cutting the stay too short. And if your design does not allow those stays, you can still use the basic idea to make a pattern. A bit of a a round about, but easy on the nerves the first few times out.
Sometimes they look pretty good (see below), but I still prefer the look of the two full-length stays. I'd think the longer stays would also give a little more flex, and be more comfortable on longer rides. But remember, if the frame is for you, do it however makes you happy.
Triangles in structures are good things. A person contemplating their removal should write himself out an explanation -- longhand and triplicate -- as to why it is necessary. Wishbone seatstays are a bad idea and exist for no reasons other than fashion and sales hooks. IMO, of course...