If I remember right from one of the videos from the SPARC reactor folks, they were experimenting with not bothering with insulation between the magnet windings. The ReBCO film is bonded to a layer of stainless steel, and they figured the conductivity of the film is so much better than stainless steel that they wouldn't actually get much loss from current leaking through. That seems kind of crazy, but I guess there's a lot of things about superconducting materials that don't behave intuitively.
Maybe manufacturers can make film that's bonded to a thinner layer of stainless steel or whatever, and thus allow for more windings in the same space?