It's officially the beginning of the end of the 32 bit Linux era as we know it, Arch Linux was the first mainstream distro to make the move, and more will now surely follow suit. Looks like it was a matter of the others (to include Ubuntu) waiting on the sidelines to see who would be the first.
This was simply an economics move, it's costly to keep up with machines that have long been last ran, many packed away in closets, many others thrown into the large recycle bin outdoors (hopefully with HDD removed & physically destroyed), and a small minority still riding out what Ubuntu 16.04 gave in two more years of breathing room, otherwise would had bit the dust in 2019.
And to be honest, it's about time, Linux cannot move forward while remaining 'backwards compatible' for years on end, thankfully Arch set the stage for the beginning of what's to come, meaning that the short term versions of Ubuntu (& distros based from it) aren't obligated to support 64 bit any longer. While the 32 bit platform has been a good one for many, just as 16 bit, and further backwards in time, 8 bit became disposable, now it's time for 32 bit users to move forward.
Not to worry, it won't be expensive, I've seen many 64 bit computers that's powerful on eBay (former corporate computers with features that consumer ones lacks) starting at $75 through $150 for a decent 64 bit PC with a Core 2 Duo, and sometimes (like my Optiplex 780) a Core 2 Quad. Note that many of the Core 2 Duo/Quad series at the end of the run were running DDR3 RAM, which my Optiplex 780, complete with a C2Q 9650 (that I grabbed for $114) does. So there's lots of hope on the horizon for those who cannot afford brand new 64 bit computers, many ships with a warranty, and replacements parts are plentiful. So if one can save only $10-15/month, in a year that's enough to purchase a good refurbished PC from a reputable seller (the latter is a must) There's hundreds of millions of these computers (both notebooks & desktops) stored in warehouses, although I don't recommend to purchase a refurbished notebook.
Because the three times I did, all resulted in a refund by SquareTrade, who handles eBay's warranties on computers at a reasonable price, a $350 model, a $100 one & finally a $400 model, since these cost more to repair than were worth, was refunded within 5 business days each. Haven't had any issues with desktops, because these aren't slung around all over the place, purchasing these are the same as an off lease corporate vehicle, the driver often could care less.
So my main recommendation if refurbished are PC's, these costs less & are easier to maintain, and best of all are 64 bit computers with late Vista Business or Windows 7 Pro (the latter preferred) installed.
In closing, it's simply time to let go of the 32 bit computers while there's a large selection of 64 bit one to choose from, before 32 bit lets you go & there's fewer & higher priced options. Today's market is a buyer's one, there's no reason for anyone to be running a 32 bit PC. Just one soda or cup of coffee per day for a year will more than pay for a 64 bit computer.
One thing that cannot be taken away are memories, yes there was a time when one could pull a working computer out of a dumpster & throw most any version of LInux on it, however those days are long gone. Please move to higher ground before you're required to. Even Mozilla Firefox 53 will stop working on some 32 bit computers & it will be very soon.
Looks like having a 32 bit computer today is as holding a hot coal, time to let go & move on!