IRC, freenode, #hurd, 2011-10-16:

<youpi> it'd be really good to have a 64bit kernel, no need to care about
  addressing space :)
<braunr> yes a 64 bits kernel would be nice
<braunr> i guess it wouldn't be too hard to have a special mach kernel for
  64 bits processors, but 32 bits userland only
<youpi> well, it means tinkering with mig
<braunr> like old sparc systems :p
<youpi> to build the 32bit interface, not the 64bit one
<braunr> ah yes
<braunr> hm
<braunr> i'm not sure
<braunr> mig would assume a 32 bits kernel, like now
<youpi> and you'll have all kinds of discrepancies in vm_size_t & such
<braunr> yes
<braunr> the 64 bits type should be completely internal
<braunr> types*
<braunr> but it would be far less work than changing all the userspace bits
  for 64 bit (ofc we'll do that some day but in the meanwhile ..)
<youpi> yes
<youpi> and it'd boost userland addrespace to 4GiB
<braunr> yes
<youpi> leaving time for a 64bit userland :)