I think Shanks just adopted Roger's way of life but with little twist.
Roger didn't care about anyone as long as no one attacked them
Shanks does the same + he tries to keep the balance of the world.
I mean clearly Shanks directly gave the strawhat to Luffy on Roger/Oden/Rayleigh/etc's orders. They knew the chosen one was coming (Luffy), and so they probably trusted Shanks with that.
I still think we could potentially get a twist that Blackbeard is actually doing everything to defeat Imu, but he's doing it in an extreme way because he realizes how important of an issue it is (essentially minmaxing his way to hopefully beat Imu and the world government), and that when Shanks and Blackberad have the fight where we expect shanks (and mihawk) to die, it could turn out that shanks wins and becomes a villain. He certainly as luffy's mentor and inspiration could very well fill the spot of a man villain as well if not better than blackbeard. (or heck, shanks shows up after luffy defeats blackbeard to kill blackbeard when everyone is hurting).
I don't think it's a sure thing, but I think it's a definite possibility. It sure would explain why aokiji and blackbeard got together, both being actually good people in a horrible situation, cuz like, if blackbeard is truly evil, I don't see how aokiji could ever feel safe since he's the most like obvious "spy" ever. But if both actually had the same goal, that'd change everything. It's the aokiji x blackbeard dynamic that I think is the strongest piece of evidence that blackbeard might not be as bad as we think. (which could be true without shanks being a villain, but shanks being a villain would be a cooler twist than just him dying as a way to hype up blackbeard)
But yeah, shanks being related to rocks or imu would be a nice way to build up Imu or Rocks and continue the tradition of family lines.
Since both Momo and Oden have the voice of all, it could be assumed that it's a hereditary thing (my guess is void century royalty, like 3-5 families). Since Roger had it, we can assume Ace had it (which could explain why whitebeard felt ace was selectively capable of being pirate king). SInce Luffy has it, Garp and Dragon probably have it too (and they honestly should with how important and swole they are)
I'm going off on a tangent, but it'd be a nice way to explain how Shanks and Kid have become (and will continue to become for Kid) so relevant. Kaidou is a dragon or some ancient dragon or oni race, Big Mom through whatever means (we don't know her parents and stuff) is a freak of nature, Shanks having strong bloodline (would be kind of like roger to adopt ie take in rocks or imu's kid and not care who they are), Buggy is clearly God, and Whitebeard we will have to learn more about. Family seems to matter in one piece though.