I think the current iteration of Steel Hunter shows how it can work without having a reward vehicle to grind, and possible ways it could be made permanent

The current daily missions are perfect to give people a decent motivation to play the mode everyday, while giving pretty decent rewards for relatively easy missions. For times where we don't have the battle pass, the missions that give us BP points could give us rewards akin to daily missions such as a med kit, extinguisher, etc.

One more change i'd add if it was made permanent would be to make it so that we rotate between maps every hour or two so that we can play when the map we like is on rotation (I personally enjoy Arzagir more than the other map)

All in all though, I think it'd help the game to have a game mode where you don't need to worry much about things like arty fire or team coordination and just let loose for a bit, kind of a game mode where you can effectively vent frustrations, and Steel Hunter is just that.