As an old FITS person, let me remind you that FITS is first for data
exchange. Since many operating systems and compilers do not support
64-bit integers (other than in sneaky hidden ways to read large
files), we should move extremely slowly to explicitly allow them in
FITS. I cannot code my machines to read or use these things, so you
cannot code your data in them if you wish my software (used lots of
places) to understand you.

I suppose I could convert a 64-bit image into double precision float
which would be inaccurate but usable. But an NAXISn or a pointer in a
heap table - those must be accurate or they do not work at all.

FITS has always been practical rather than "modern" - let's keep it
that way.

Eric Greisen