Do you think 343 Should allow the community to come up with new armor ideas for future armor?
Simply, yes.
They do, some of the time. They rely on us to pinpoint issues within games, and sometimes they take on full ideas. For example, the Memories of Reach update was based on an idea suggested on YouTube, called Remember Reach.
A lot of armor is refurbished armors from HALO 4 and others.
Yes. They already are, but I think it would be cool if they allowed people to submit armour ideas (Kinda like what RoosterTeeth did with one of their RWBY characters).