Thank you for your suggestion. We will look at adding this to the feature request list.
For mountain bike users I would suggest to develop a tool to highlight the routes tagged in Open Street Map with MTB tags and show their rating: i.e. mtb:scale (0-6); mtb:scale:uphill (0-5): mtb:scale:imba (0-4). This would allow users to understand if a track/path is suitable for MTB and how difficult it is.
Probably using an additional map layer with a dedicated rendering for MTB users could be a good option. You will find an example of such a rendering in openmtbmap.org