I think the primary difficulty is that it will eat up valuable real estate in the summary box.
Notice the column layout of that pane; the right column with the numbers in it can't drift over into the left column with the stat.
To do what you want would have to increase that box width by at least 10 or more characters. Not such a big deal on a 2500x1600 screen, but I'm pretty sure this screen is optimized for something not any larger than 1280x768, and that's a lot of space to give up.
Take a look at how cramped the current planet summary screen is at the minimum resolution: go to Options, set your resolution to 1280x768, and then start up a new game. There's really no extra space for even those 10 characters.