More tile size options? Sure. On the bigger screen, the 4x4 looks pretty good. I'm probably the only one but I'd also like a 1x3 or 1x4 option- I'd use this for a mail, message or calendar live tile where I just need to see two or three long strings of text. It could also work well as a divider/header tile (until we can create actual groups like in W8).
Background images? I'm not a fan myself but if that's what people want to do... I wouldn't mind getting a few more color options (maybe gray), but I find images kind of distracting. I love my rotation of lock screen images- and I even find I prefer to keep things simple there- too much stuff and it takes away from the photo. Once I get to Start I don't want further distractions or clutter or tiles clashing with a wallpaper. Going back to my old iPhone I realized I really preferred the stock wallpapers (or something equally unobtrusive).