The XS proposal before the BF offers the following:

lo is defined as the generic article

1. We need intensionality and don't have a style that's agreed upon, and this lo can cover those cases
2. In most usage it has been used as the generic
3. We don't need an extensional alias for da poi; we can use su'o for that
4. It will actually retain most or all of the properties which the Book assigns it