It would be helpful if fixed spaces were not automatically treated as non-breaking. I often use fixed spaces to finesse typographic issues—like a lowercase "f" crashing into an uppercase letter that follows it (e.g., "if I"), which seems to happen a lot, even in reputable fonts. I don't however, necessarily want InDesign to prevent a line break after the fixed space.

Ideally, we would be able to have breaking and nonbreaking versions of all of the fixed spaces, but perhaps it wouldn't be very useful for hair or thin spaces. Ems, ens, thirds, fourths, and sixths, however....

Thanks for considering this.