How to fit the new SSJ4 in Super

Dragonball Daima IS canon. The main canon is...

Dragonball Manga (Pilaf saga to Buu saga)

Dragonball Daima

Dragonball Super Manga (comprising Battle of Gods and Superhero manga arcs)

Resurrection F

Broly Movie

The rest, even Dragonball Super Anime which is more canonical than the rest of it, is either minor canon, either non canon.

But the last Daima episode made a mess with SSJ4.

First, after it looked like a form Goku obtained through magic and did not have in Super due to lack of a tail, it turns out he unlocked it after Buu saga by training. However he did not train his Oozaru form to regain consciousness to get it, and he did not even have a tail at all. SSJ4 was treated as if it was literally SSJ"4", the final evolution of the golden forms line. How could it be red and have a tail then ?!

However, here I want to show how Goku could actually have had it through Super, while never ever using it.

First here is a multiplier list

SSJ ×50

SSJ2 ×100

SSJ3 ×400

SSJ4 ×4.000

SSJG ×40.000+

SSJB ×200.000+

MSSJB ×2.000.000+ (SSJG ×50)

SSJBE ×4.000.000+ (SSJG ×100)

As you see, SSJ4 is very distant from both SSJ3 and SSJG. We know from the Beerus fight SSJG is at least ×100 stronger than SSJ3. It could be SSJ3 ×10.000, but that is beyond the point here. Since Goku during the whole Daima apparently had it but did not use it until the end, he likely treated it as a secret weapon. This is why we saw it only by the end of Daima.

When he fought Beerus 3 years later in Battle of Gods, he went through all the SSJ levels, but as a SSJ3, after lying about SSJ3 being his strongest form, he got knocked down. Then he realized Beerus was way way stronger than 10 times SSJ3, which made SSJ4 obsolete before it was used ever again. He even argued Beerus to be stronger than SSJ3 Gogeta, who would have been easily avaible.

After SSJB Goku never needed anymore anything stronger than SSJ2 except for SSJB itself due the great Ki control SSJB offers. He only used SSJ and SSJ2 for weaker foes, and used SSJ3 only when he wanted to be exactly at 400 times his Base. SSJ4 was only a secret weapon but it got replaced by a much better secret weapon. So Goku not using it ever is consistent with the way he did not use it through most of Daima.

When could SSJ4 be used again ? It would NOT be consistent if suddenly Goku starts to use it post Superhero arc VS stronger than SSJ3 but weaker than SSJG minor foes. To use it he would have to have his God Ki drained. Since the new SSJ4 apparently has a tail but Goku unlocked it without one, a no tail version could be used by Caulifla and Gotenks, but not by Kale, and not by Broly or Gohan, because LSSJ and Beast form are immensely more powerful than 10 times SSJ3.

I think Gotenks will never have it because after Buu saga he became essentially comic relief, and in the last Movie, as an adult, he also gained 200 pounds of fat. So if we would ever see it again it would be if divine forms somehow got restricted and Goku had it as his best form again, or if Caulifla is shown again.

However, I find simply absurd how you do not need a tail to unlock it, yet the form does have one. This makes the disappearing and reappearing nipples and shirt look like a minor thing in comparison. I reckon Universe 6 Saiyan should not have a tail anyway while using it because they are not born with monkey genes at all, having lost them through evolution. The GT version made way more sense, I believe they should just have canonized that. Neva could have turned Goku into a Golden Oozaru, and then he would have turned SSJ4.

If U6 Saiyans are shown again, Cabba should have SSJ3, and Caulifla SSJ4, mirroring Vegeta and Goku before God Ki. Having tailless Saiyans have it is the only good side of this new SSJ4 compared to the GT one.