IIRC this has been announced as well couple of months ago.

Why do you want a 64-bit client?

We’ve spent most of our lives living in the 32bit paradise

This is a completely different thing, Steam is dropping support for 32bit operating systems. Fedora hasn't had a 32bit release since version 31. What that proposal was about was dropping 32bit packages, which would break old 32bit games (and Steam itself, as it relies on a lot of 32bit libraries as well).

I remember being so excited for 64bit Far Cry. Had no idea what it meant. But I was excited!

And when 64-bit support first came to Windows, Microsoft artificially limited the amount of RAM you could use unless you shelled out for the much more expensive editions. On Vista you were arbitrarily limited to 8 gigs with the basic edition, 16 with premium, and even the business editions had a limit of 128 gigs, a tiny fraction of the addressable space under a 64 bit architecture.

Even now there's a limit, though it's insanely high (over a terabyte) and you're unlikely to ever see it unless you're running a server on Windows instead of Windows Server (still limited, but in the dozens of terabytes) or Linux (which has a "limit" in the petabytes).

That'll probably follow soon after, but I don't really see the benefit, it's not like Steam needs the extra memory or registers...

In that case, your OS (Windows) can run 32-bit apps. The Steam application itself won't have a 32-bit version at some point soon.