I would think it would be hard to get the wires in a location where it would be possible to do a good joint. I am often barely able to get a soldering iron into a space to work without burning up a bunch of other wires, occasionally I still touch and slightly melt the insulation on surrounding wires.

The only reason most of my wire splices work is that I am able to twist the wires together before I heat the joint so I don't need to support the wires at all during the soldering operation.

Though, it would be nice to have a splicing operation that would have an insulating sheathing in place at the end of the soldering operation.