Perhaps try using position absolute or fixed and align it to the right side
.navbar .navbar-toggler{
position: absolute;
right: 0;
}
You should also consider moving collapsible content outside of the nav
<nav class="navbar navbar-light bg-faded">
<a class="navbar-brand" href="#">My Brand</a>
<button class="navbar-toggler float-xs-right" type="button" data-toggle="collapse" data-target="#exCollapsingNavbar" aria-controls="exCollapsingNavbar" aria-expanded="false" aria-label="Toggle navigation">Expand</button>
</nav>
<div class="collapse" id="exCollapsingNavbar">
<div class="bg-inverse text-muted p-1">
<h4>Collapsed content</h4>
<span class="text-muted">Toggleable via the navbar brand.</span>
</div>
</div>
Check out the updated plunker