In chapter 1028 we see Sanji develop exoskeleton and regeneration powers, similar to what his brothers also have. It’s important to note that those abilities are standards between all four brothers and are not a specialty for Sanji.
What is a specialty for Sanji is the Stealth (invisibility) that his raid suit gives him, hence his name “Stealth Black.”
I bring this up because I noticed that during the fight between Sanji (Stealth Black) and Niji (Electric Blue), Niji used “Henry Needle” without a raid suit on. This means that it is possible for the brothers to use their specialty moves whenever they want, without the use of a raid suit.
This opens up the possibility for Sanji to be able to go invisible without the raid suit. Because remember the fire he can conjure is NOT his Germa specialty, it’s something different.
Since the suit is unlocking some of his Germa abilities it might also give him the ability to use the Stealth aspect of it as he pleases.
If this does happen, then Sanji will have all the following abilities under his belt:
1-Fire Conjuring, 2-Invisibility, 3-Extreme Durability, 4-Regeneration, 5-Flight, 6-Super Speed on Land and Sea, 7-Super Human Strength, 8-Haki.