Raspberry Pi should be looking to the future, breaking free and adopting RISC V for future Pi.
I think there was an interview where Eben did talk about RISC-V, so don't rule it out.
There is a few RISC-V chips around now but I don't see any matching GPUs.
RPT is still a small engineering team, design a new RISC-V chip with GPU?
Not going to be quick to do, there are much lower risk options.
Besides, is it "The Mission" to designs chips?
Quite few people have now done Aarch64 spins and a lot of that is being upstreamed.
Most major Linux distributions will probably have Aarm64 spins for Pi's by the end of 2018.
This will lower the need for a Raspbian64 OS as people will have a multiplicity of choices
Raspbian is for teaching, I started learning Linux with it and have mostly moved on to other OS's.
Raspbian got me comfortable with Linux but using PiCore made me really learn basic Linux and shell scripting.
Gentoo now is making me learn a whole new version of 64bit Linux, no big deal.
A Debian64 version would have been nice, but not important.
Important for me is learning Aarch64 and all the improvements it can bring to Machine Learning.
Why do people want 64bit OS?
Those who really, really, really want ARMv8A don't have to wait for a Raspbian version.
The hard part has been done, just proving that it can be done
I'm dancing on Rainbows.
Raspberries are not Apples or Oranges