4 years? That's just an instant. We'll be there before we know it.
I'm with Dropbear on that, I have lots of (very) old DOS/Windows games I still like to play every now and then (don't like new stuff), and this will influence my choice of distro: I'm on Mint right now, but when Mint (due to Ubuntu) goes 64-bit only, I'll have to move. I don't want to, but I need the OS to run my programs, not the other way round.