I won’t be buying one for the moment but I mention it for another reason. 4 GB is the maximum RAM that a 32-bit OS can use, and on the PI like on Windows it’s actually 3 GB. To be fair you can have two processes each with 3 GB on the 8 GB Pi.
The announcement did mention that a beta 64-bit Raspbian OS is available for download and it’s here. This article shows that the 64-bit Os they tested is faster on the Pi than 32-bit. This link to the DietPi forum tells you how to boot dietpi into 64-bit.
It’s to be hoped that 64-bit ARM development software will become available. Clang and gcc should be but I’m thinking of the code.headmelted.com version of Visual Studio Code.
As always if you are buying a Raspberry Pi 4B, I strongly suggest you get a case with a fan. They are not expensive and do make a difference. Despite running the Asteroids game, which is pretty intense, I have never got my 4B temperature above 51C. THat said I’ve ordered a touchscreen with a case for a 4B on the back and it doesn’t seem to take a fan. So it will be interesting to see what its like fanless. More on that when the touchscreen arrives.