That's the wrong question to be asking. The relevant hardware change is when x86 CPUs that don't support 64-bit code finally disappeared from the market and eventually from the install base.

There is only a very narrow range of use cases for which running 32-bit code on a x86-64 processor is preferable to running the same code compiled as 64-bit. For everything else, going 64-bit is a clear improvement if not an outright necessity. Even if it didn't require any ongoing maintenance, continuing to ship 32-bit versions means wasting storage space and network bandwidth, and leaving on the table the improvements enabled by going 64-bit (eg. better ObjC runtime). For the entire existence of x86-64 processors it has been clear that retaining 32-bit compatibility through the entire software stack has significant downsides and that the cost/benefit balance has been inexorably moving toward eventually dropping 32-bit support.