Whonix is my last shred of 32-bit for a few years now, and my personal vote would go to 64-bit. That said...
I know from having had multiple layers of performance issues with KVM and VirtualBox I'd never run the Workstation on a CPU from 32-bit era anymore. But Gateway you could.
For reference, OpenSUSE Leap was released as 64-only, comparable to Debian. Your edge cases might look like: https://forums.opensuse.org/showthread.php/510584-Missing-32-bit-version-of-new-openSUSE-42-1-%28 - 9 year old Mac that shipped with 32-bit firmware despite 64-bit CPU, Skype, some PCs from 2008-2010 one guy says. They mention Windows 7 users who got 32-bit installs, which I recall happened quite a bit in the beginning.
Biggest question: people in developing countries?
Personally the only use case I could picture for myself is wanting an old clunker to use as Gateway for physical isolation.