I have a Jamis Citizen 2 Step through (2013 or 14 maybe) which has a braze-on on the underside of the seat stay near the brake studs. Just one braze on each side. I'm curious as to what the intent is and what opportunities they enable. I already mounted rack and fenders so I'm not talking about the brazes near the seat tube. In the photo behind the link look closely and see the braze-on just on the inside of the back wheel.
Here is the bike:
Zoomed in photo highlighting the specific braze-on: