Developing such a feature would take a big effort and a long time. As you said the compiler needs to be changed and so does the C library. All the ramifications need to be considered. One needs to consider how many people would benefit. Newlib-nano already has a mechanism to have floating point support in printf and scanf optional which provides better reward (more code saved) for less work (change in compiler is only a nice to have to automate the selection of float code).
All in all, I don't believe we can justify working on this for the time being.
Developing such a feature would take a big effort and a long time. As you said the compiler needs to be changed and so does the C library. All the ramifications need to be considered. One needs to consider how many people would benefit. Newlib-nano already has a mechanism to have floating point support in printf and scanf optional which provides better reward (more code saved) for less work (change in compiler is only a nice to have to automate the selection of float code).
All in all, I don't believe we can justify working on this for the time being.
Best regards.