I think you're making some very wrong assumptions... firstly, ubuntu is not a "Leading Edge" Distro, whatever that means, its goal is to bring linux closer to the masses, they chose debian as their base partly because of the broad range of architectures it supports. dropping support for 32-bits goes against that goal.
You're also completely off base in implying that ubuntu is unfit for older computers, it runs as well as most linux distros on older hardware. Yes ubuntu offers the latest eye-candy features, but many of its users disable them, I use ubuntu because it's a breeze to maintain, it stays out of my way, and its very popular and well supported, so I know I'll be able to find help when I need it.
I think requiring 64 bits is a completely unreasonable requirement, and would affect WAY more people than you realize. Sure there are other distros that will support 32 bit, but tbh, I dont want to run them, I've tried many of them and none are as pleasant as ubuntu, I'm not about to give that up because of your dim-witted notion that 32 bit computers are obsolete.
On top of that, the whole idea dropping support for an architecture seems downright stupid unless you're totally sure there are only a handful of them in existence. that is clearly not the case with 32-bit x86 cpu's, and it wont be for a VERY long time.
TL;DR you can pry my 32-bit CPU's from my cold dead hands.