Make the horizontal width of the flair customizable to any arbitrary size.
This was apparently a feature of StackFlair or other alternatives, but according to this answer here, they are no longer available. I think this is a valuable feature to add to the official version.
My personal issue that causes me to wish for this is that I have exactly eight(8) SE sites that are presently above 200 rep, while the flair can only show exactly seven(7) icons. Thus, the numeric values are including exactly one(1) more site than is shown. Of course, one can always be "one-off" from the default amount by poor luck, but that seems like all the better reason to allow any arbitrary number of sites of the user's choice to be shown.
My image above shows the inconsistency - I am shown to have 8 gold badges on my flair, as I have exactly 1 gold badge on each of 8 sites (all Fanatic for each). However, it only shows 7 sites. Thus, my badge total is inaccurate for the sites shown. It would be great if I could simply make the flair wider, and thus show as many sites as I wish.