Not so good. . . : ( Similar looking cracks are seen in these posts . . .
Delamination is blamed.
Is the crack skin deep or all the way thru the roof panel??
If thru the roof panel then the crack needs to be both stopped and stabilized.
Drill a tiny hole just beyond where the crack is propagating to . . .
Are you able to access the other side of the roof panel? If yes then create a stainless steel sandwich that will stop any vibrating across the crack. Maybe 3/4" by 1-1/2" top and bottom with SS screws to hold all together.
If only skin deep can a sealant be added under the delaminated area??
Then your Eternabond proposal can be applied over everything for the final waterproofing/caulking.
Hope your repair proceeds well.
2012 Rockwood A122,
2017 Kia Sorento 3.3 V6 AWD ,
2012 Subaru Forester with MT (gone to TV heaven)
Cheers and greetings
from a Toronto Canuck