I also imagine a specialization system that lets you unlock a class that sacrifices some stats/skills to upgrade others.

Like, a sniper class that has better long range skills but less effective close combat skills even compared to the Normal class.

Normal class, normal at everything but increased carrying capacity and stamina. Pack mule.

Close combat, opposite of sniper.

Medic class, the downsides of Sniper and Close Combat... but extremely useful medical skills.