Dragon Ball Super: Super Hero finally gave Piccolo a new transformation, but it might not be his last or strongest. While neither "Orange Piccolo" nor "Gohan Beast" are apparently canon at this time, it's entirely possible that they could eventually become so. However, the movie's wording makes it seem like this may be as powerful as Piccolo can get. Dragon Ball and Dragon Ball Super, on the other hand, suggest otherwise.
Piccolo gains his new form just before the film's climax. Around the midpoint of the movie, he recalls the Unlock Potential ability that Guru used on Gohan, Krillin, and Dende, all the way back during the time of the Namek Saga. He then gets Dende to modify Shenron so the eternal dragon could do the same for him. When the battle against Dr. Hedo's supposedly superior androids, the Gammas, goes south, Piccolo awakens his brand new, bulky, citrus-colored transformation, Orange Piccolo.
While this form is formidable, it's likely that Piccolo can become far stronger. If the power increase is consistent with other instances of it in Dragon Ball Z's Namek Saga, there's no reason to think it's Piccolo's peak. Not only that, but Dragon Ball Super showed one definitive way that Namekians can absolutely get strong enough to compete with their Saiyan counterparts.
How Piccolo Can Get A Stronger Form After Orange
The increase in Piccolo's power appears to have come from a wish to Shenron. However, Piccolo's new transformation wasn't actually part of that wish and was presumably an extra gift to Piccolo from Shenron. It showed that Piccolo is as capable of getting swept up by hot blood as Goku, as he didn't use the remaining two wishes on anything to more simply resolve the Red Ribbon Army situation. The name of the Unlock Potential ability is also confusing, Shenron said that Piccolo only had a "little bit" more power to bring out, but that isn't how Unlock Potential works. The Unlock Potential state is a flat increase that taps into an individual's full power at that time, not their lifetime potential. Otherwise, Gohan would likely have beaten Frieza on Namek by himself.
Dragon Ball Super's Tournament of Power went the extra mile in showing one admittedly dark way that Namekians could become as powerful as Saiyans. The Universe 6 fighters, Saonel and Pilina were a pair of Namekians who, in their effort to win the whole thing, fused with many of the other Namekians from their universe. This gave them power enough to compete with the likes of Ultimate Gohan, who was about on par with Super Saiyan Blue Goku. Piccolo has already fused with the likes of Nail and Kami, and he has gotten stronger since then. While it's unlikely that Namekian Fusion will come into play for him again, the option is there. It also wouldn't necessarily have to be permanent. If the Dragon Balls could split Shin and Kibito from the Potara-fused state, then Namekian Fusion might be on the table.
The Dragon Ball Super manga recently showed during its Granolah Saga, that the Unlock Potential ability is distinctly different from tapping into all the potential one will ever have across their entire life. Both Granolah and Gas proved that with their wishes, or Elec's wish, in the case of Gas, on Toronbo. That, along with the ever-present possibility of more Namekian Fusions means that Dragon Ball Super: Super Hero's Orange Piccolo is nowhere near as powerful as the nameless Namekian can get.