No; the assumption is that the user runs one application,
Now, if you take MicroB or Modest. With those applications it isn't feasable to use them full screen because the functionality withers. MicroB does not support tabs, and the settings or favourites aren't easily accessible.
BTW, we'd also need some standardization on gestures.
Why I would want to access brightness settings while using an application is beyond my understanding. Its definetely not something I'll be doing daily. Besides, brightness settings should be static, like a good pair of glasses does with sunlight.