In the playtest package humans are the only race without a "subrace" despite being the most diverse and adaptive race. And, because they're less of a "hook" for the race and racial powers humans get very blank bonuses.

What about changing that? Say, taking a page from Dragonlance and having "civilized" or "barbarian" humans. Give one a bonus to mental skills and the other a bonus to physical skills. Add new powers accordingly, such as hardiness or wilderness survival powers for one and others suggesting intelligence and decadence.

The names are flexible. "Urban" and "nomadic" would work. As would "urbane / erudite" and "wild / rural".

It instantly adds some distinction to humans. The suggestion of story and world building. Humans aren't all identical
There are the savage Cimmeria and the softer south folk. There are the Northfolk and the southern people beyond the wall. The hardy barbarian tribes of the traders from Ten-Towns. There are the rough Germanic folk or the culture Romans.