He's not going to have any more scientific power-ups, he never wanted any and it's something that's been imposed on him. Anyone talking about germa or vegapunk power-ups is delusional.
His next power up will focus on his flames and haki, so either oda reveals that his current flames are just a small part of his true power, which is likely given that he's been teasing sanji's firepower in the last few sbs, or he gets a haki boost to support hotter flames, or just increases the AP/DC of his attacks.