There's no point in attempting to get your idea out, 343i know what they're doing, it's very unlikely that they'd impliment some change from a fan. Just stating the solid facts, I'm sure there are a lot of us that want something specific in Halo 4 but we don't work for 343i, thus our thoughts/ideas arn't important. Hmmm, I don't think a map 3 times the size of forge world would be good at all. I'd rather a map a little smaller than forge world and the ability to use 5 times the budget.
Anyway, if I had an idea I guess the main element I'd like to have in Halo would to have a lot more choice in forge, with structure, vehicles, buildings... more of everything!