Dragon Ball Super introduced the Super Saiyan Blue form. Could a Super Saiyan Blue go Super Saiyan 3? It’s possible. It would also be dangerous.
Dragon Ball Super introduced the concept of Super Saiyan Gods — a hyper-powerful new transformation that augmented a Super Saiyan. Unlike previous Super Saiyan transformations, Super Saiyan God forms were not simply the next form in a line of transformations, but stood alongside the other Super Saiyan forms. They’re similar to the Kaio-Ken technique, which could be compounded with the pre-existing Super Saiyan form.
This led to the Super Saiyan God Super Saiyan form — otherwise known as Super Saiyan Blue. Super Saiyan God forms resembled the normal base Saiyan form, but Goku and Vegeta came to realize they could then harness their Super Saiyan forms while in Super Saiyan God form.
While Goku and Vegeta kept trying to push further beyond this form — as seen by both the Super Saiyan Blue Kaio-Ken form and Ultra Instinct form — fans have theorized that both Goku and Vegeta could push even further beyond: combine the Super Saiyan God form with Super Saiyan 3.
Super Saiyan transformations expend a great amount of ki. Radiant auras spray energy out in bursts strong enough to bust open planets. This is true for the Kaio-Ken as well, which multiplies an individual’s energy while putting a strain on the body. Part of Goku’s training as a Super Saiyan is to maintain the Super Saiyan form as a base form, allowing him to better access their abilities.
Transforming into a Super Saiyan 2 or 3 drains Goku of energy and strength. In the Buu Saga, Goku is only able to maintain the form for brief intervals of time, while Gotenks’ transformation into Super Saiyan 3 consumes so much energy it significantly shortens the length of the half-hour fusion.
From this information, it could be assumed that the different forms consume different levels of energy, but the reality is that all Super Saiyan forms are the same form, pushed to greater extremes. Because of this, Super Saiyan 1, 2, and 3 aren’t separate techniques, but the same technique, just with extra, channeled energy.
In a June 2014 interview in Saikyo Jump, Akira Toriyama confirmed that the Super Saiyan 3 is not in fact a separate form, but rather a hyped-up version of the Super Saiyan transformation. “Super Saiyan 2 and 3 are nothing more than powered-up variations of Super Saiyan. After the fight with Beerus, Goku realized that mastering his normal state and Super Saiyan would raise his level more and sap less strength, so I think he probably won’t become Super Saiyan 2 or 3 any more.”
In this sense, when Goku becomes Super Saiyan 3 in the Buu Saga during Dragon Ball Z and the whole planet starts shaking, the uncontrollable aura is a demonstration of Goku’s weakness, not power. It shows that Goku has incredible strength but very little control of that power.
Super Saiyan Blue is essentially the product of Goku determining a way to utilize the Super Saiyan technique while transformed as a Super Saiyan God — the pure mastery of the Super Saiyan form. As Toriyama implied, mastering his Super Saiyan state allows Goku to control the loss of ki that erupts from his body.
Super Saiyan Blue is a demonstration of Goku and Vegeta’s mastery of both separate techniques. This is why Super Saiyan 3 Vegeta will probably never pop up, because Vegeta has already mastered his Super Saiyan power and surpassed the limitations of Super Saiyan 3 without developing Goku’s unstable power-leaking weakness. Because Super Saiyan 3 is not a separate technique from the normal Super Saiyan technique, Super Saiyan Blue represents the power of Super Saiyan 3 without the power-leak and with extreme control over energy.
Could Goku push his power levels to its utter extreme, creating an unstable power-leaking form that resembles Super Saiyan 3 with blue hair? Possibly. However, consider that Super Saiyan God alone can almost ruptures holes in reality in Dragon Ball Super. If Goku were to lose control of his power as a Super Saiyan God as he does as a Super Saiyan 3, then it’s highly possible that, by virtue of existing in this form, reality itself could break down.
Super Saiyan God Super Saiyan 3 would represent Goku losing control of his power, not necessarily growing more powerful. He wouldn’t destroy his opposition, but rather the reality in which that opposition exists. Nothing in the universe would be able to stop him… because there would be no universe!