All the inconsistencies you suggest sound like a trap, especially when you suggest ABI and API behaviour divergences. From what I understood of your macro idea

All the inconsistencies you suggest sound like a trap, especially when you suggest ABI and API behaviour divergences. From what I understood of your macro idea this would lead to API changes that would lead to ifdefs for different (g)libcurl versions. Doesn’t feel good especially for software distributors. Also the changes you mention require changes in the linker scripts distributed by a variety of toolchains and would need to check if the libc target was a blessed one. In effect the deprecation would never move to obsolete and kept around forever. To clarify the above post libc is in control of dynamic linking through the dl*(dlopen) family of functions.