I drive antique vehicles which are often slow but i don't mind driving on highways so dont want to check "avoid freeways", i would just like that the navigtion algorythm takes my top speed (50mph for one car 65 for the other one) into account when calculating the route.
this could be set in the "type of vehicles" menu, select "special" and have a customizable "top speed".
then, even on a 80mph road, waze would only consider i'll make 50 and maybe reroute me on a shorter path !

If you want to go further you could even set a "garage" in wich we set each of our our vehicles (cars, motorbikes, ...), their fuel and their top speed. it would popup at the app launch, and at travel planing, and allow us to keep all settings in memory.
sorry for english mistakes...i'm french....