The gap between the end of the Dragon Ball Z anime and beginning of the Dragon Ball Super series is still filled with storylines and power-ups that were either left unfinished, or never made it into the official series canon. One of the biggest loose threads has no doubt been the Super Saiyan 4 transformation, which was a big focus of the Dragon Ball GT series, but has never actually been an official part of Dragon Ball canon. However, while Dragon Ball Super might ignore Super Saiyan 4's existence, the form has maintained iconic status, thanks to continued devotion from fans.
Case in point: this gorgeous piece of Dragon Ball Super Saiyan 4 fan art has not only captured a lot of attention for its visuals - it has reignited the discussion within the fandom, about what should be done about SSJ4!
If you check the discussion thread on that Reddit post, it pretty much tells the tale. Dragon Ball fans are burning some serious torches for Super Saiyan 4 - and rightly so. While on the one hand, SSJ4 did start to push Dragon Ball into a somewhat gimmicky series of number-based transformations, it also reconnected the series Super Saiyan form to the Great Ape form that helped define the original series. SSJ4 opened the door to new intrigue about Saiyans and the source of their massive power potential - and though Dragon Ball Super has explored that question on a divine level (with Super Saiyan God, Super Saiyan Blue, Ultra Instinct), the darker, more beastial side of Saiyans deserves just as much attention (if not more).
Best of all (and as many fans are aware), Dragon Ball Super has already set the stage for Super Saiyan 4 to be officially confirmed as part of canon. Dragon Ball Super: Broly revealed that Broly's limitless power and berserker rage was explained by his father Paragus as being the ability to channel the power of a Great Ape through his human form. Broly developed that (power? Mutation?) after Paragus forcibly amputated his tail as a boy; since Goku and Vegeta both lost their tails, it stands to reason that Broly's version of Super Saiyan 4 is also within their reach. Granted, given this revised version of the form, the actual canonized look of SSJ4 would be different than what Dragon Ball GT introduced - but different doesn't necessarily mean worse.
The Japanese-language and English dub releases of Dragon Ball Super are now complete and available to stream with FunimationNOW and Crunchyroll. Viz Media is releasing new chapters of the manga at a monthly rate that can be read entirely for free through the Shonen Jump digital library, and Dragon Ball Super's big movie, Dragon Ball Super: Broly, is now available on Blu-ray and DVD. Fans in Japan are also able to enjoy fresh non-canon adventures from the franchises with new episodes of Super Dragon Ball Heroes' promotional anime series.