ETE custom calculation

[Esteban90]

Hi, I don't actually know if this is already possible to do, at least I haven't found any setting.
Anyways, what I think would be interesting, is to be able to set a formula to calculate a customer ETE whenever a route is planned with BRouter or similar.
Something like the implementation of this rule of thumb for hiking time:

For 1 km of hiking: allow approximatively 15 minutes.
-   For 100 m of ascent: add an extra 15 minutes.
-   For 200 m of medium-steep descent: add another 15 minutes .