Reinforcing what kingosticks is saying, until there’s an 8 GB Pi 4 (which I’d buy in a second!), there’s no compelling reason for a 64 bit OS. 32 bits can address all of the memory a 4 GB Pi 4 has. I’d love the whole system to move toward a 64 bit OS, but I don’t really see the point of the overhead of 64 bit code on a 4 GB address space.
That’s not to day that I don’t toy with 64 bit OSs on my Pi 4, I’m just not sure where the pay off is today.