Yes, Elastic with list view or at least list view above preview pane would be great.
The new theme looks great and being a responsive design it works quite well on my smartphone. Unfortunately the width of the mail list is quite narrow. Subjects longer than a few characters are not shown in full. In fact, I get
more text width by making the window
smaller (because on small display sizes the preview pane is not shown)! Even on a fullscreen (Full HD) the maximum text width is smaller than when not displaying the preview pane.
An option for having the preview pane below the list, or not displayed at all (on all display sizes) would be perfect.