Will the new skills auto change depending on level?

I was taking a look at the changes to jobs for 4.0 and see that skills will be upgraded, bard for example, with the level 64 trait "Bite Mastery" Venom Bite and Wind Bite are upgraded to Caustic Bite and Storm Bite respectively.

Does this mean that we only have to have the 2 skills and not 4 on the hotbars? and they will change automatically via level sync?

Presumably, yes, just one button that works just like we want.

Yup, but just for specific skills. For instance, Stone will upgrade from rank I to IV saving up to 3 slots. And if u do a low level dungeon it downgrade to the appropriate rank