Probably modules is a more fanzy buzz word for chapters. 🙂 And indeed most will play the complete set of modules, although we are already ignoring battle tactics and the terrain effects already in third.
I can't imagine I would play without commands, magic, army composition and command models. Imo it would be a rather dull and barebone game.
It will be interesting to see how the game works with all the modules, but without the magic module. There has to be something added to compensate the loss of magic for Soulblight, Tzeentch, Lumineth and etc..; . If the same warscroll is used for everything except Spearhead. The effect of losing the Magic module seems huge for some armies.
Edit: I was wrong as it seems that the Magic module is included in everything, except spearhead. Lol, I already find it confusing.
Edit2: PTG seems to most interesting option for casual players. Everything is in there except battle tactics, although than chosing the first turn has no more drawback anymore as BT aren't a thing. Lol.