While the Juggernaut has proven himself to be an unstoppable force of chaos and destruction in his base form, he is completely ignoring an upgrade that would increase his power exponentially and make him one of the most powerful beings on the planet.
Cain Marko became the Juggernaut after discovering a mystical crystal inside a hidden temple while serving in the United States armed forces during the Korean War. Little did he know, Marko found the Crimson Gem of Cyttorak which granted him incredible strength, speed, stamina, and invulnerability. By accepting these powers, Marko also accepted his role as being Cyttorak’s human juggernaut, and would be forced to bring about destruction in the demon-god’s name. Cain Marko, who already proved he didn’t have a very strong moral compass, accepted the role without question and thereby officially became the Unstoppable Juggernaut.
In New Excalibur #15 by Frank Tieri and Jim Calafiore, the Juggernaut had grown tired of being a villain and instead wished to do some good with his powers, so he joined a team of heroes to fend off a deadly threat. However, because of his change of heart, Cyttorak decided to put Marko up to a new test to see if he was still strong enough to be his vessel of chaos on Earth. During the trial, the Juggernaut faces another being who was also granted the powers of the Crimson Bands of Cyttorak, though instead of simply fighting with his fists as Marko does, this man fights with a sword. Since he is wielding this weapon, the challenger Juggernaut is seemingly able to channel Cyttorak’s unstoppable momentum through the weapon as it is strong enough to pierce Juggernaut’s armor and even injure him with a single slice, something not even adamantium can do.
If the person who wielded Juggernaut's power could imbue his sword with the power of Cyttorak, that implies that the Juggernaut could do that with any weapon he so chooses. This would be a huge upgrade for the character, as the Juggernaut isn’t very effective with long-range attacks (despite the fact that he is perhaps the deadliest person one could ever meet face-to-face). If the Juggernaut decided to use a heavy artillery weapon like a bazooka, for instance, and passed on the magic momentum that makes him unstoppable... then he would become a truly god-level Marvel supervillain. Plus, with his apparent inclusion on the X-Men off-shoot team of Nightcrawler's known as the Legionnaires, the Juggernaut will have a whole squad of mutants in his corner with the entirety of Krakoan technology at his disposal to create a weapon best suited for him. Basically, Juggernaut would become a walking tank with unlimited ammo and an eternal power source.
While Cain Marko may not be so inclined to change-up his fighting style, his apparent successor may be up for the upgrade. In the upcoming X-Force #28, it seems as though the Omega-level mutant assassin Quentin Quire will be taking up the mantle of the Juggernaut, and his go-to attack is telepathic firearms that he can conjure on command. While Juggernaut’s powerful upgrade may have been teased in New Excalibur #15, it may actually come to fruition in X-Force #28. However, likelihood of the Juggernaut actually implementing this obvious improvement remains to be seen, and as it currently stands, Juggernaut is completely ignoring an upgrade that would truly make him unstoppable.