If Trip explains how Gurdurr evolved into Cokeldurr, then maybe Ash could do the same. I mean, who the hell would Trip trade and trade back with? The only person I could think of would be Juniper :/
Tbh though, Boldore didn't evolve that long ago
I'd prefer a starter evolution from Oshawott/Snivy over Boldore becoming Gigalith..
I'd rather him evolve right before the league or in the potential filler, maybe he trades it to Oak for something? Or maybe he Oak's it and it evolves under Oak's care like Brock's Onix... Or maybe there's a special cave in another region or something >_<