32 bit users are going to have to be cut off eventually. Or does everyone really imagine they'll be playing DF 1.0 on a 30-40 year old computer?
It depends on how much management it needs, but if it's enough to impact the schedule it'd be insane to keep ensuring 32 bit compatibility for the next 20 years. Why bother going 64 bit in the first place if there's no plans to ever take advantage of it?
Well, hopefully someone will eventually hack up a 64 bit XP clone for those insistent that it can't be beaten.
I put together a version of linux mint on the computer downstairs for the in-laws since they're longtime windows users, and mint has an XP skin that only confused them when they noticed it wasn't actually windows.
The biggest issue with sticking to 32 bit isn't performance, it's security, there are significant improvements from using WOW64, 64 bit registers, and various 64 bit architecture based security features whether you're using a 32 bit program or not. Clinging to an OS/hardware combo which is so old that it can't be updated to 64 bit means you're waaaaaay out in "I've got literally no security beyond obscurity" land, and it's unfortunate but that isn't a large portion of the user base, nor is it one which a developer should feel obligated to continue supporting. I can fully appreciate being broke as a joke, but you could probably find a computer being tossed out somewhere that would run 64 bit OS/software combos. It isn't like this is a looming thing, it was 10.. 11 12 years ago.