If a height slider was applied, I don't think presets of heights should be implemented. Keep them as they are as a base and then let the player decide how tall or short they want their Sims because many adults, including myself, are no where near 6ft tall. :)
But like @jmattgaming mentioned, the animations and interactions with other Sims and Objects would have to be considered. There's quite a bit of variety of scaling to consider with animations so that would be a large task. In no way am I putting limitations on the devs or the game, just stating that it would probably need some coding overhaul.
