If you start with a small layout and then you try to enlarge it, you'll find out that Construct doesn't draw outside the layout even though it's zoomed, which makes sense (this could be useful for the Black Bars thing).
So you'll have to also enlarge your layout. But since your layout is larger now, you'll also have to scroll it. I'm still working on the math for that, it goes all weird tho, there's some bugs around. So far, scrolling to the center of the original layout size works for me, but you gotta set scrolling to unbounded (BUG?), and if I set the scroll from the same function object event I use to change the resolution, it won't scroll.
I shall post a .cap with all of this. Soon.