On another topic I proposed this:
But.
We are currently giving options to change some sizes (avatars and wrapper width off the top of my head) from the admin interface, forcing these changes only on one (or two) of the multiple media queries present in the theme.
I start to believe (well, not really start now, I already started a while ago) that these settings may not really be worth the hassle.
There is a custom.css file available, I would be tempted to encourage people to do these changes there.
It may be worth adding a sample file with few rules including all the media queries necessary to change the sizes in all the variations.
I don't need to change avatar sizes. ;)
So long it won't overflow and stick with 100% of its parent, then it should be fine with just default css.