English has some vestiges of the grammatical dual, in terms of having a special word for the case of two: both vs all, either vs any, neither vs none. (And for real pedants, between vs among.)
Dual doesn't really help in this case. In a dual system, we would have something like:
1 pant
2 pantx
3+ pants
The problem with the words op is describing is that they should, semantically, belong to the category of 1 object, but morphologically (and syntactically) belong to the category of not-1 object. Adding a separate category for 2 objects does not address this.
I occasionally dabble in the spoken-out-loud “glassen” and “panten”. I should do it more.
Also lot's of languages when borrowing from English do away with the plural if it's obvious. Like in french, a pair of jeans is just un jean, singular.