Te reo enters the chat... 'eh' is pronounced pretty close to 'nei' and can have a similar meaning in some contexts when used after an opinion (to add a slightly rhetorical emphasis). I think there is a possibility that eh is an anglicised version of nei. maoridictionary.co.nz/search?&keyw...

Good thought & appropriate While you are here, maybe you can help clarify whether the old Nya Zild "hooray" as a farewell, as possibly coming from e noho ra, which the Colonial Anglophone ear might hear as "hoorah" & adapt I've long had this theory but my linguistics MA wife will have none of it

Or at least that may have contributed to the uptake here of eh