I think the name Jack...
Is actually related to his real name.
Like a pet name for either John or Jacob.
A list of suspects with those names:
Montague John Druitt
Jacob Levy
Dr. John Williams
Or a play on the the letters of his name:
[JA]mes Maybri[CK]
without the [c]:
[JA]mes [K]enneth Stevens
[JA]mes [K]elly
Personally, of those six, I think the most likely to be the ripper are:
James Kelly
or
Jacob Levy
This is probably all just silly, but I thought I'd throw it out there anyways and see what others think about it.