Fixed Spaces Automatically set as Nonbreaking
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.

-
John Bishop commented
I have just had this exact problem in a book I am preparing - I use a nonwestern font a lot, and third spaces were really useful in finessing typographic issues in that particular font - but the fact that they were non-breaking caused real problems for the justification.
I see that Matthew's post is five years old - is this something that is still being considered?