I'd like to get to know Marlon more. He's a really intriguing character for me, I almost get a father/mentor vibe from him. Its really sad that he never leaves the guild except on holidays. I'd like to see him around town more or in the tavern. I'd also like to see mini-events around the guild where he's training the character in combat or sharing old stories of his adventures. I think I may try to mod this in myself, but I also thought I'd drop the suggestion here to see if it gets traction. Thanks so much for stardew valley, I love it!
I also noticed that he has a thing for Marnie at the flower dance. This could make for an interesting triangle with between him, Lewis, and Marnie. I just see Marlon and I think, "this guy has some cool stories." I'd really like to get to know him better xD