Grand Sanguine equipments can be looted from the Bakragore bossfight while cursed by Bakragore's final taint. That means you and your team need to kill Bakragore once, redo all minibosses with the final taint, then kill the final boss with the final taint + all 4 normal taints.
As you can imagine, this is quite a task and as far as I'm aware no teams in all worlds even tried killing the final boss in this condition. It is just too risky, too early (teams are still learning how to do or optimise the bossfight) or players are just too low level for it. I could be wrong but it will take some time until we start seeing the first attempts.
In the mean time we can use what's already known as speculate a bit, and one thing that is known is that there are 5 different ids for Bag You Covet in the game.
Both Soul War (Bag You Desire) and Primal Ordeal (Primal Bag) only have one id for their respective bags. If you quickly think about it, there's no real reason for more to exist, right? There are no different equipments, no different mechanics that could affect them... Nothing.
The Rotten Blood Quest on the other hand has its peculiarities however. If we try to "reverse engineer" the idea of having 5 different ids, that means we need to have 5 different purposes for each of them, otherwise CipSoft is just adding chunk to the code, and if I quickly think of ways one could acquire one of these bags we have:
That gives us two alternatives BUT I just mentioned a team can use taints to modify the potential loot from Bakragore, so that gives us three alternatives: Crimson Offering, Bakragore + Minis (without final taint), Bakragore (with final taint [doesn't affect minis]).
Okay, we are missing two ids and here's another piece of information: If you read the teasers or details provided by CipSoft related to this quest, they informed us the first bag looted from Bakragore has way higher drop rate than the next ones a player would loot. That likely means CipSoft needed additional ids to make some sort of if statement to check whether a player looted their high chance drop bag or not. If they didn't, roll the die for the high chance drop bag, if not roll the die for the low change drop bag.
With that we have my speculation on why there are five different bag ids and they are:
- Crimson Offering
- High chance drop bag (aka first Bag You Covet a player would loot)
- Low chance drop bag
- High chance drop Grand bag (first Bag You Covet containing a Grand equipment)
- Low chance drop Grand bag
So answering your question, Grand variant equipments are looted from Bakragore when it gets killed by players with all taints (all 4 standard + final taint) and it's very likely that they come in a Bag You Covet and not loose.