Hello cyrilp,
I would rather try using Camera Station concept, providing that properly calibrated nodal head (or similar equipment) is used for each camera location.
Extremely large images should be subdivided internally during the main processing stages, so it should be possible to process accurately stitched panoramas. However, I can't remember if I previously heard of such experiments with 8 gigapixel images processing in Metashape. At least it is not something regular.