So after 24 hours with Title Update 8 and the Warlords of New York expansion, here are some spoiler-free thoughts.
Most of the following concerns the Warlords expansion, where you can now level up gear to 40. However, to a lesser degree much of this still applies.
If you've got a bunch of saved builds, none of them will work quite like they did before. You don't have to get rid of the gear itself (yet), but don't kid yourself that your Dark Zone or raid builds are going to be useful anymore. Now is the time to focus on getting better stuff. This is even true without the expansion, since the maximum gear score is 515.
Focus on leveling up and getting top tier gear. Try out the new brand sets and get familiar with the new talents.
Gears mods now affect only one attribute. Skill mods always trigger but scale based on your skill level, which can range from 0 to 6. These two changes can have surprising effects on old builds.
It's much easier to try out gear talents. Sadly, only vests and backpacks have them now. But swapping to a piece with a different talent is simple compared to before.
Exotics now have a singular talent. And that talent is in almost all cases a shadow of what it once was. All those wonderful holstered talents are a thing of the past.
Don't feed gear into the recalibration unless you're dealing with top tier gear. If you're not jumping into the expansion, you can start, but the bench library has two tiers: level 30, and level 31-40. So once you do head into the expansion, the bench library won't be helpful. For gear and weapons in the expansion, you should start putting items in the library the moment they start dropping with talents. Since talents are not leveled, you can save them even on gear that's not level 40. The attributes of gear below level 40, however, will all be well below the maximum, so it's not worth the effort to save them.
If you're playing the expansion, your main focus should be completing the campaign and getting to level 40. On that journey you'll get a lot of gear and weapons. Do not save any gear you are aren't actually using. Sell or dismantle them. You and your stash will thank me later.