Dynamic Module dependency injection

I am trying to do something fancy: a DynamicModule that chooses a Controller/Providers depending on a provider. The provider reads a config in a DB at onModuleInit, so there is no way to hard-code its values.

It is similar to this issue: https://github.com/nestjs/nest/issues/601 which was never answered...

I have tried a few approaches and the closest I have got is this:

export class FancyModule implements DynamicModule {
  public module: Type<FancyModule>;
  public controllers: Type<unknown>[];
  public providers: Provider<unknown>[];
  constructor (
    @Inject(StartupConfigService) private readonly startup: StartupConfigService,
  ) {
    this.module = FancyModule;
    if (startup.featureFlagEnabled) {
      this.controllers = [ FancyFeatureController ];
      this.providers = [ FancyFeatureService ];
    } else {
      this.controllers = [ ErrorController ];
      this.providers = [];
    }
  }
}

Second approach:

app.module.ts

@Module({
  imports: [
    StartupConfigModule.register(startupConfigOption),
    FancyModule.registerAsync({
      imports: [StartupConfigModule],
      useFactory: function (startupConfigService: StartupConfigService) {
           return startupConfigService.config
      },
      inject: [StartupConfigService],
   }),
 ],
})

fancy.module.ts

export class FancyModule {
  static registerAsync (config: IAppConfig): DynamicModule {
    if (config.featureFlagEnabled) {
      return {
        module: FancyModule,
        controllers: [ FancyFeatureController ],
        providers: [ FancyFeatureService ],
      };
    } else {
      return {
        module: FancyModule,
        controllers: [ ],
        providers: [ ],
      };
    }
  }
}

This injects as expected but the controllers and providers are never spun up. Is the meta-data evaluated before the constructor? Is that a bug?