I'll try to hit everything that was questioned, so sorry if I miss something.
The update is considered minor as it doesn't actually affect any of the game play other than the decrease in pick 6s, and that adjustment was easy because there is one check that determines if the player returns the ball all the way on an interception. There were four different checks for this depending on where the ball was thrown, deep or short and in between. The shortest two checks were pumped up way more than the medium and long checks. After looking at some results, it was pretty easy to tell that the short pass pick 6 chances were a little too much, so I adjusted them closer to the medium and long pass checks and ran some tests on the results and pick 6s are down some. There are still probably too many pick 6s and they still might seem more random than tied to ratings, but I wanted to get those adjusted before we go into update lock down while working on the engine update because when looking at a lot of "random upsets" there were many times that the random pick 6 seemed to do the damage. This is mostly a band-aid to stop a little bleeding until I can fully adjust that logic with the engine update. But it is very, very minor and will not impact how you play the game.
The other real change is the split of the game plan settings. These I've tested pretty considerably and even though it looks like a major change, it is actually pretty minor because of the way we load the playbooks. Essentially now instead of just loading one set of game plan settings into the engine when simulating a game, we also load a set of defensive game plan settings. Playbooks are loaded into the engine the same exact way, but determining which playbook you are using will check the offensive game plan settings or defensive game plan settings depending on which side of the ball you are on. When the update is pushed out, both offense and defense game plans will be set to your current settings, so if you do nothing with them when the update goes out your game plans will act EXACTLY the same as they do now.
The other changes to the depth chart pages are not actually changing any values or settings, but just exposing the values that are being set under the hood with your selections. So when you see "Fairly Fresh (85%)" rest level on the fatigue settings, it was already being set to 85% rest level. You just didn't see what that value was, so this is to help with making better decisions with those settings. Likewise, a Rush setting of "Level 4" was internally 60%, but you had no idea what relative rushing chance you had between Level 3 and Level 4. So now you will know what the relative value is for rushing chances. These were simply UI changes so there was relatively little testing needed.
The RB Depth Chart will have locked in values of 100% which will be displayed for reference against your other settings. This is exactly how it works now, equating to a locked in "Often" setting, but it was never displayed on the Depth Chart.
I can't check every world to see where they fall on your schedule, but you should be able to tell. It will be implemented after the second half of the 4/18 games. Whatever game is after that will be the first game with the changes. Again, if you change nothing, everything will behave exactly the same as it does now.
Since the only effect on the engine is really just a minor tweak and all the settings that changed behave the same as they did before, I'm okay with pushing this out and immediately taking effect. For more extensive changes, especially the engine update, I will always try to stagger the implementation between seasons, like we did with the Formation IQ. The most difficult part with that is when UI changes as it's more difficult to have different worlds using two different UIs than it is to control which version of the engine they use. But for the engine change, I will definitely work on not springing that on anyone in the middle of the season as it will definitely affect how games play out.