That's a great idea Carlo. We'll look into that. For now though, if you select HILLS to display the elevation profile in the route planner, it should show you when on the route you are when you move your mouse over the elevation chart. This should help with adding directions in the relevant places.
Plotaroute has "almost" everything I need. What I miss is the possibility to add a direction clicking on the Hills profile. That would be very useful in order to add a "summit" or "valley" points, that, while riding will let me know how far is the end of uphill or downhill.