Inhumans have existed in the MCU for the last few years thanks to Agents of S.H.I.E.L.D., but their 'Nuhumans' do not have the same knowledge of their purpose as the Royal Family on Inhumans. Back in season 2 of S.H.I.E.L.D., the series introduced the presence of Inhumans into the MCU by transforming Chloe Bennet from Skye to Daisy Johnson aka Quake. Since that reveal, the Inhumans population has continued to grow, thanks in large part to the end of season 2 - where Terrigen became infused with the ocean's food supply.
The fallout was a major story of season 3 and saw an influx of Inhumans characters to the cast. While they all know that they are Inhumans, they do not have the entire history of their race available. Inhumans will look to change that by introducing the Royal Family, with one of their arcs tying back into this older S.H.I.E.L.D. storyline.
Showrunner Scott Buck confirmed this to be the case while speaking to CBR about his next Marvel endeavor. He confirmed that Triton (Mike Moh) has been sent to Earth - as shown in the Inhumans trailer - to investigate the Terrigan outbreak that has seen the Inhuman population on Earth skyrocket. But, Buck also explained that the Inhumans Triton is used to dealing with on Atillan are far different from the 'Nuhumans' that now populate Earth:
We have seen ‘nuhumans’ on Agents of S.H.I.E.L.D., but this is completely different. These are Inhumans who know exactly who they are and know the importance of their powers. They know the importance of their Terrigen ceremony which is the holiest, most ritual ceremony in their civilization. I think the ‘nuhumans’ who inhabit Earth have no idea what’s going on. They are distant relatives of our characters.
There has yet to be any official confirmation that the two ABC properties will have character crossovers, but they clearly both exist with the other in mind. Considering all of S.H.I.E.L.D.'s main players are currently in space, there is probably not a strong likelihood of Triton being given the chance to pass on this knowledge to the Nuhumans. However, the exploration of Inhumans and their individual purpose in Inhumans could create greater backstories for their 'distant relatives', as Buck states.
Any connective tissues to S.H.I.E.L.D. that Triton's story will have will not not the only example of the shows living in the same world. The Inhuman markings that have been prevalent in S.H.I.E.L.D. since season one, have repeatedly been seen on the set of Inhumans, as well as on the royal throne. Even without direct crossovers, Inhumans could still add depth to previous S.H.I.E.L.D. stories, or hint towards their future adventures as well. With a direct crossover possibly being out of the question, S.H.I.E.L.D. fans who tune in to Inhumans may only get these smaller connections for now.
Marvel’s Inhumans premieres in IMAX on September 1, before the series begins on ABC on September 29. Agents of S.H.I.E.L.D. returns for season 5 in January 2018.