We're always considering new categories and this has been one that has been brought up by users before.
A lot of modem/routers are lumped into the Routers category.
For example, the TP Link 8816 Modem Router I have is on this site.
Maybe try look through that section!
I tried adding my modem to the router category and it got rejected. (it does not have a router in it) That's why I suggested a category for modems.