I think the whole Nika possession thing is still a huge possibility. It doesn't make sense for Gear 5 to have no consequences. G2 drained Luffy's stamina, G3 made him small, G4 took his haki, but G5 has no negatives? it especially makes no sense when we were outright shown that Kid and Law's awakenings drained their stamina and they awakened even before Luffy did.
Obviously as a zoan, Luffy's awakening won't have the same consequences as Kid and Law's. As crocodile said, awakened zoans have higher stamina. However awakened zoans also kinda lost their minds.
Which is why imo Nika possessing Luffy is even more likely than ever. It would be the consequence of Luffy overusing G5. If Luffy overuses G5, he goes into a rage mode and nobody would be able to stop him. This might be why we only see Kaido's crazy eyed form(which bares semblance to Luffy's eyes in G5) for 1-off attacks. Kaido might not be able to spam his awakening without going into a rage and killing people.