Changing Shove to an action and making it a spell container where you can choose between shoving 5ft or shove to prone can be done easily by mods.
In fact, there are already mods out there that do that. I dabbled a little bit in modding the game (and made a mod only for me, with such changes), stuff like changing the cost or effect of a spell or ability is very, very easy.
So Larian could change it anytime and it would cost one of their developers only like 5 minutes of working time - that they have not done it yet, means they like how shove plays out, IMO.
