I would like to have the option to change the road surface roughness factor before selecting a route to gravel, dirt, cobbles, pavement, etc. This would be cool because you would have to push more watts on some surfaces to keep the same speed. And this could be applied in group rides. For example, a cat B rider could join a cat C ride and apply a different road surface roughness factor to make it harder. There are lots of possibilities with such a feature!
Just ride a mountain bike on the pavement and a road bike in the jungle.
or a gravel bike on ANY surface . 
But it would be nice to ride e.g. the jungle, with a road bike on tarmac, if I wanted to.
Before it was a “gravel” route that was my favourite efforts training circuit too .
Or ride a TT bike in group rides… you will end us pushing the most watts to maintain the same pace