I don't think there would've been any way to make a different form of Gholdengo when the only actual lore difference between Roaming Gimmighoul and Chest Gimmighoul is that Roaming Gimmighoul is just the creature itself without a chest while Chest Gimmighoul is the creature living in a treasure chest of coins that it uses as cover and to gather coins in itself.
Gholdengo's entire thing is that the creature that Gimmighoul is essentially fused with the 1000 coins it gathered, including the one it carries on its back, and evolved into a new form made of gold. Gholdengo is literally a body of 1000 coins.
The only thing I could argue is that Roaming Form Gimmighoul that evolve into Gholdengo should have a minor aesthetic difference where they don't have a treasure chest wrapped around their waist, but there would be no feasible stat changes. The only notable thing denoting Chest Gimmighoul that evolve is that Gholdengo has the Gimmighoul chest attached to a waistband wrapped around its waist after it has outgrown it but still holding the chest dear to it, but Roaming Form Gimmighoul didn't have any treasure chest to live in before evolving so that aesthetic difference of those Gholdengo not having one would be sensible.
That said Gholdengo no matter what fundamentally holds the same lore and even the minor aesthetic difference wouldn't change its stats because its defenses come from it being made of gold and the treasure chest doesn't bog it down in any way like it did for Gimmighoul. Chest Gimmighoul was slower because Gimmighoul lives in the chest and the thing can barely move, but gives it protection, while Roaming Gimmighoul are mobile but individually are frail.