I felt like the Jenkins/Lee 12-parter back in 1998 (I think it came out under the Marvel Knights banner?) was pretty close to what this might look like - I'd have to re-read, but if memory serves, there weren't any outside characters, aside from the humans who found Attilan.
I'd check it out as well - Eternals and Inhumans have always been my personal two favourite Marvel franchises - but I think history has already proven that Marvel could take them out of the regular continuity and still do something interesting with them. a move like that would probably make more financial sense for them than selling off the rights completely, but I'm not an economics major either lol, so what do I know?