Some way to load and maybe save NBT structures to the same place that structure blocks save and load them from.
Or load the NBT files from any file location that its allowed to access.

Maybe a function like structure_load(structureName, locationArray, [rotation], [mirror]) to load a saved structure into the world.

So if I use a command block to save a structure named "minecraft:test", i could load it with CommandHelper using
structure_load("minecraft:test", ploc("Steve"))
to place it at Steve's location for example