I was looking into how best to insert some layers from Sketch v43 JSON. I had to do some mucking about w/ private headers & hopper but I came up with this:
var page = {/*json from decompressed sketch file */};
var decoded = [[[MSJSONDictionaryUnarchiver alloc] initForReadingFromDictionary:page] decodeRoot];
var msPage = [[MSPage alloc] initWithImmutableModelObject:decoded];
context.document.currentPage().addLayers(msPage.layers());
It would be really nice if there were a more supported / correct way to do this as part of the API.
But huge props for taking this to the finish line, I know you've been working hard on it for a while ?