A disproportionate amount of the crew seems to be Irish, Scottish or Japanese

[flyerdog]

In the future, new surnames may arise the same way existing ones originally did; from occupations, transliterations, misspellings, legal name changes, etc.

Yeah, that's most likely. As people of different background "mix" there would be some surname 'sharing', you might see a crewmember who is African descent with the last name "O'Donnell" as one of his African ancestors paired up with someone from Dublin etc...

 

[WarpTenLizard]

Here's an idea: perhaps one of the Maquis colonies was an Irish or Scottish community, like the one Beverly Crusher's nanna lived in. Janeway and Carrey are just Irish by coincidence, but a handful of the others are former Maquis from the same colony. There might also be a Japanese colony as well, contributing to the high number of Japanese surnames on Voyager.