Just forget BMi because the FFP should disappear next year.
Korean Air is an interesting case : you can "just" fly 500k miles with Delta or any SKyteam partner and being Morning Calm Premium for life giving ELite + status.
The negative time you won't get any status if you don't fly till you reach the 500k unless you you fly at least 30k miles with Korean AIr every two years.
So it's only worth it if you can wait till you get it and care about any sor of bonus miles.
It might be interesting to know what gift is offered to Million Milers every year.
Does anyone know anything about this?