The cost of turnbuckles is one of my pet peeves, but on really lightweight structures their weight is not inconsiderable either, especially when you add all those nicopress fittings.Thanks for the encouraging words PT, I think this could be adapted to wire bracing also, but who can afford the price of turnbuckles these days?
But I am pursuing an alternative that would work well with your idea: Custom spokes are available from a lot of sources; high strength, with rolled threads and they can even be had with swaged down diameters. Cost - anything from about $1.50 to 2.50 or so, less in quantity. Carbon or stainless. Now spokes lead a very hard life; constantly changing and high loads. Despite the apparent crudity of then bent over, swaged head, it has stood the test of time. Now picture your fittings with a lug extending for attaching a spoke, one in each corner of a fuselage bay. This is where the bent head of the spoke attaches, same as on a wheel hub. Bring the threaded ends towards the middle and join them using a ring cut from thick walled tubing, drilled to hold four regular spoke nipples. Super-light and efficient and even cheap.