How much software is still running 32 bit binaries that won’t be recompiled because the source code has been lost together with the build instructions, the compiler, and the guy who knew how it worked?
How much software is using int32 instead of time_t, then casting/converting in various creative ways?
How many protocols, serialization formats and structs have 32 bit fields?
How many UNIX machines in production are still running on machines with 32-bit words, or using a 32-bit time_t?
How much software is still running 32 bit binaries that won’t be recompiled because the source code has been lost together with the build instructions, the compiler, and the guy who knew how it worked?
How much software is using int32 instead of time_t, then casting/converting in various creative ways?
How many protocols, serialization formats and structs have 32 bit fields?
Irrelevant. The question you should ask instead is: how many of those things will still be in use in 15 years.