Bonus Rolls in the Great Vault
As mentioned previously, Bonus Rolls will be available from the Great Vault at the start of the Season 2. Players will need to complete at least 3 filled-slots in a week in order to claim the reward. Additional bonus rolls will be available weekly starting on Week 8 of Season 2.
When Bonus Rolls were added in Season 1, they weren't done so at the start of a season meaning that Bonus Rolls were catch up to a lot of players, and weren't used directly for the gearing process as much. However, with Bonus Rolls being an option from the Great Vault (almost) right away, players have found a very optimal strategy, but it comes at the cost of a very boring Great Vault every week -- taking nothing but the Bonus Roll every time.
The Very Boring Optimal Strategy
Because of the many changes to End Game gearing, many players are currently planning a very boring strategy, because it seems optimal -- only taking the Bonus Roll in most cases.
The Reasoning
Bonus Rolls in the Great Vault are already powerful, and way more impactful than a lot of the "pity" currency items that players could get previously get where if you got a bad vault, you were basically grabbing a socket. However, due to the way the Bonus Roll system works and additional changes in Season 2, this makes Bonus Rolls in the Vault even more powerful:
The Item Level of the Bonus Roll is not stored based on the slots you unlocked. You could complete 8 Tier 1 Delves, and then bank a Bonus Roll to roll on Mythic boss and win a Myth 6/6 piece.
Bonus Rolls have a knockout list that does NOT consider items acquired in other ways. This means that if you take Tier Gloves from the Great Vault, you can still roll Tier Gloves off of a Mythic boss which would waste a future Bonus Roll.
With the raid reward changes, where Heroic raid drops Myth loot in the Vault and Mythic raid's Vault now dropping Myth 6/6, Bonus Rolls are even more impactful on this front. Using a Bonus Roll on the last boss of Heroic with all the amazing cantrip loot, will result in a Myth version that would probably last you a long time (until you defeat Mythic Ul'atek).
As a raiding example: if you only clear Heroic on the first week of Season 2, but expect to kill the two bosses of Mythic the following week, you can take the Bonus Roll (avoiding Myth 1/6 gear) and then Bonus Roll the first or second boss to get a Myth 6/6 piece of gear, saving 80 Myth Mistcrest!
Taking a Piece of Gear
There are some times where you would want to take a piece of gear directly from the Vault though. The main one will be when it's your last Best-in-Slot or impactful item from a boss. For example, if you only needed one specific trinket from a Mythic+ dungeon, then it's probably worth it to grab it because the you'll never need to Bonus Roll that dungeon ever again, and it's way more efficient than bonus rolling through a bunch of loot you don't need.
The only other time that you may want to consider taking a piece of gear is if you want the power NOW. If you have a massive upgrade, and you really want that power right now in order to overcome a challenge, you may decide it is worth it to risk bonus rolling a duplicate item later. I suspect that many people will not be interested in doing this, and it would be rather rare for an upgrade to be that massive for a lot of players to consider it, but it is an option to consider in some cases.
Other Impacts
There is one other major impact that Bonus Rolls in the Great Vault may cause -- raiders will likely be less interested in doing Mythic+ for Vault Slots later on. Mythic+ will still be a fantastic way to gear up for raiders in the early season, as Mythic+ is the only way to get uncapped Hero gear early in the season. However, once we start getting deeper into the Season, unless players are searching for a few specific Mythic+ trinkets or items, we may see raiders completely abandon Mythic+ altogether, as there is no reason for them to ever want something in the Mythic+ row, and all they need to do to get their Bonus Roll is to fill 3 boxes which will probably be raid, but could be Tier 1 Delves or even World Content.
Mythic+ will still be a good way to get Myth Mistcrest and Hero gear, but raiders may lose interest in Mythic+ earlier this season due to the Bonus Rolls.
In addition, for a lot of players this may completely negate the feeling of an exciting vault on reset day. One of the most exciting times of the start of the season is opening your vault and seeing what the RNG gods have started to bestow on you, and then sharing it with your friends and guild. There was even an addon that would make it more exciting, but if players are going to take Bonus Rolls, then there is no group excitement anymore.
There's also some imbalance between specs and classes when bonus rolling, as some specs have all items they want to hit, and some specs have items that have some misses in the mix. It's not the biggest deal in the grand scheme of things, but it's something that is worth mentioning.
Solutions
What can be done about this? Many players have suggested that taking things from the Great Vault should remove the item from the knockout list of Bonus Rolls. This would definitely help, as if you see an item that you want, you would take it, and then you can't get it again. This definitely makes the Vault more exciting week to week once again, but Blizzard has mentioned in our group interview that this will not be the case for Patch 12.1, but they have heard the feedback.
While I think this would help, the other main issue is banking a Bonus Roll for higher item level. In a very extreme example, a character can do 8 Tier 1 Delves and then eventually get a Myth 9/6 item. While many players would be happy with that, it's definitely a little odd. There's an interesting choice in power now versus power later as Paul Kubit mentioned in the interview, but the case for "power now" is very very small for a lot of players, and the possibilities of "power later" are much much larger. We saw from the Puzzling Cartel Chip chip system in Patch 11.1 that many players didn't want to use their tokens until they had access to the highest item level piece, and it's likely that this will be similar. I expected players to bank their Bonus Rolls until they can get the maximum value from them, and many players won't even consider looking at a non Myth 6/6 vault if they plan on killing a Mythic boss at some point in the season.
