Gary finally debutting must obviously merit some significance in an episode featuring Moltres. I'll find it hard to belive if Gay loses to Moltres, seeing how he Has electrive and his strongest pokemon, Blastoise, which competiviely by stats and typing has a Huge Advantage over Moltres.
Although his Blastoise did lose to charizard, a pokemon of the same dual type as moltres, this was mostly because Ash was given charizard strategic commands to counter Gary's blastoise offensive attacks. However, since Moltres, is wild and doesnt have a trainer to aid it strategically in battle like Ash did, I dont see Gary's blastoise losing.
I see these scenario's, Goh challenges Moltres, and loses. Then Ash, and it'll possibly end in a stalemate. Gary will challenge it with Electrive, but will then use his strongest pokemon Blastoise to finish it off.
Ash will then realize, that Gary will be packing a jugernaut team, which will inspire Ash to catch more pokemon, and possibly legendaries in order to diversify his team.
I remeber in an interview a while back, how the creator of Pokemon (Satoshi) mentions, how Gary's role in the anime, is sort of like a mentor and master for Ash. I dont know if he feels the same way as he did before, but Gary's debut will definitly change Ash's progression in the story.
As for Goh meeting Gary, I can see Goh having an inferiority complex when he realizes how knowledgable Gary is more than he is when it comes to Pokemon.