Tenacity as a defensive stat will have no place outside of potentially ultimates.

Tenacity as an offensive stat will change not at all. Melds will still be like this:

If BiS Crit breaks even with DH or better: Crit > DH > Det > Ten; SkS only to reach GCD sweetspots.
If BiS Crit too low to theoretically beat DH: DH > Crit > Det > Ten; SkS unchanged
If playing ungabunga / WAR: Crit > Det > Ten / SkS > DH.

TL;DR: Tenacity is an ok stat, just not one viable to focus on.