Yes, armor to go with her would be lovely! But only in small areas in heavy amounts, which is partially what I went with in her design. You can see an exposed core in the middle of her chest there.
If she had a shield, it would make a lot of sense for it to be extremely resistant or even indestructible, but she wouldn't be a big attacker on her own~!
I really like the sound of Colossus, but she wouldn't be a mark X~! Once I redesign her (for the third time, it would seem) I intend to... ya know, actually save the model, so I can make higher Marks for her~!
I think she'd be super cool as a miniboss. Maybe appearing periodically between things like endless stages, or as part of her own challenge! :3