gistfile1.m

// view model
self.figureOutWhatToShowNext = [RACCommand commandWithCanExecuteSignal:self.okayToShowNextThing];
self.nextVM = [[self.figureOutWhatToShowNext addSignalBlock:^ RACSignal *(id value) {
  return [self.model.figureItOut map:id (id x) { return x.boolValue ? [[OkayVM alloc] init] : [[NotOkayVM alloc] init] }];
] flatten];

// view

someButton.rac_command = vm.figureOutWhatToShowNext;
[vm.nextVM subscribeNext:^ (id vm) {
  UIViewController *vc = makeVCFromVMSomehow(vm);
  [self.navigationController presentViewController:vc animated:YES];
}];