So what's the running theme between Loki and Blackbeard's DFs?
Imu has some kind of DF or power. BB's DF has the ability to negate other DF users making their DF powers weaker in contact with his DF. Loki still has chapters to show the full abilities of his DF but it was definitely needed for whatever reason to make him deal with his father who Imu was controlling.
The strongest Haki user is Joyboy, followed by whoever is debatable as the 2nd strongest haki user between Rocks, Harald, Shanks, Rogers or Garp. Since he is not Joyboy level in Haki he avoided fighting Imu and even the 6 strongest signature attacks from yonkos, rocks, garp and roger did nothing to Imu. Rocks stated he would be coming back for Imu, and I am assuming he would be coming back since his goal was to find 2 DFs and a mysterious giant crew
In the end Rock's couldn't find those 2 DFs and only reason he was forced into god valley was because his son and wife were there. Blackbeard experienced Imu's power 1st hand in God valley as a kid and has knowledge on DFs so that's why I think that was the reason why he pursued the darkness DF for so long to kill a crewmate over it. Assuming if Loki and Blackbeard are in possession of the 2 DFs that can somehow harm Imu then I don't think Luffy would have a mysterious 3rd DF so maybe he will be Joyboy level in Haki in some final battle.
However, they resolve the Elbaf arc.
-Loki will be considered an ally with a DF that can harm Imu, and he might have his own crew with brogy and dorry coming back to their senses if such a thing happened, he would be considered Yonko level with his crew
-Luffy and his crew will carry on to another arc after Elbaf.
-Blackbeard is in possession with supposedly another DF that can harm Imu, Devon completed her mission touching one of the Elders and she is known for copying DFs. I doubt it has something to do with Saturn's Zoan DF having special abilities it might be related to Imu's DF ability that allows him to control others and touching the others he has control of might be indirectly touching his DF, I don't know. Blackbeard's crew looks like they will also have one of the 3 ancient DFs or 2(if Caribou knows about shirahoshi)
-Shanks crew no one knows what they will do later.
-Buggy's crew no one knows what they will do later.
-Law and Kidd are out of commission for being too weak.