Barbarian questions.

This may have already said this before. By me even.
Why would WotC get rid of taking damage for extending Rage and replace it with forcing a saving throw? Taking damage would extend my Rage, even in real life. LOL
While raging Barbarians can't maintain concentration. They also can't cast spells. How does Primal Knowledge work? Wouldn't some of the skills you are given while raging require some concentration? Maybe, some of the time?

Switching  damage to forcing a saving throw makes everything you do to extend your Rage be something you do, rather than something that happens to you. Extending your Rage by forcing a saving throw means that you can use your action to do something like Grapple an enemy and your Rage won't drop after your turn.

Quote from FoxMulder >>

While raging Barbarians can't maintain concentration. They also can't cast spells. How does Primal Knowledge work? Wouldn't some of the skills you are given while raging require some concentration? Maybe, some of the time?

Making an ability check does not require Concentration. In this context the word "Concentration" is referring to a specific rules mechanic in D&D, not to just the general concept of concentrating on things.

In 5.5e, Barbarians can also extend their rage with a bonus action, if they aren't able to make an attack or force a save.