There are some nouns that are always plurals e.g. "scissors" or "pants", and those things still arguably need indefinite/definite distinction, right? Actually no, the very use of plain "scissors" instead of "*a scissors" demonstrates very well the redundancy of the indefinite article, but let's pretend.
Again, e.g. Bulgarian uses едни ("ones") as essentially plural indefinite article, and for genuinely plural things too. It's not nearly as pervasive as the English usage (the null article is used in most cases), but it exists. While in English you could reply to "Where are you going?" with "To hang out with some friends" ('it doesn't really matter to you which ones exactly'), in Bulgarian that "some" would be translated as "едни", not "няколко" or "някои" (technically, you could use that last one, but the meaning would be that you're yourself not sure with whom exactly you're going to hang out there).
