Commit dialog default width is too narrow
The commit dialog opens at a default width of 600, which is frustratingly just slightly too small to actually fit 72-character lines with e.g., default Fedora-shipped fonts, and most other default fonts that I've seen.
An easy "fix" here would be to increase the default width to 700, which in my limited testing will fit 72 characters at a normal-ish 11pt font with enough extra space so that the right-hand margin shows.
Another option for a fix might be to do what Meld does and actually set a size request proportional to the font width. FWIW, Meld does this:
context = self.textview.get_pango_context()
metrics = context.get_metrics(font, context.get_language())
char_width = metrics.get_approximate_char_width() / Pango.SCALE
self.scrolledwindow1.set_size_request(80 * char_width, -1)
although the 80 in the last line there could (and probably should) be right margin width preference + 2
or something. The down side to doing this is that it sets an actual minimum width on the widget, whereas it would be nicer to have this set as the natural width instead.