It only won't work on modern pure-UEFI systems because that would require writing full stack of USB drivers for keyboard and mouse, and that would be a huge task.
> Edit: I understand a motivation if it is on simplicity choosing one or the other, but other than that I don't see why that should ever be a goal worthy to be pursued. Software should really "just work" no matter the number of bits and bytes.
Not really how software works.
Just sold my SGI Indigo 2 for 900 $ ! Vintage 64 bit is absolutely a thing. :-)
Personally I’d have said it isn’t. But these terms are subjective.
(That distinction wasn't clear to me either, so I had to look it up - TIL).
The last step (32-bit to 64-bit) can a bit of a can of worms especially on older platforms where 64-bit implementations can differ greatly and 32-bit "just works tm". 32-bit is quite well supported and has enough resources to make some interesting programs work without much hassle.
I think the author has made the decision not to support 64-bit mode due to needing to balance the complexity and usability of the project. It is a hobby project after all.
Since the author maintains a 16-bit and 32-bit for this project I suppose if you wanted you can always fork and maintain a 64-bit version if you wanted to.