Given that we say “at university” not “at a university” I think we can assume Uni is a non-count noun and avoid pluralising it altogether.
Although i’ve noticed the way non-count nouns are treated seems less stable, so maybe that whole thing is on the way out. Data is often treated as a plural not a non-count noun - i heard “this data is” 15+ years ago, whereas i hear “these data are” now.
I think it’s very reasonable to pluralize the abbrievation with an apostrophe though, especially since “unis” would naturally be read with a short ‘i’ rather than the ‘ee’ of “Uni”
Given that we say “at university” not “at a university” I think we can assume Uni is a non-count noun and avoid pluralising it altogether.
Although i’ve noticed the way non-count nouns are treated seems less stable, so maybe that whole thing is on the way out. Data is often treated as a plural not a non-count noun - i heard “this data is” 15+ years ago, whereas i hear “these data are” now.
I think it’s very reasonable to pluralize the abbrievation with an apostrophe though, especially since “unis” would naturally be read with a short ‘i’ rather than the ‘ee’ of “Uni”