Some theme ideas:
Computer virus/glitch. A warframe who intermingled with Orokin/Corpus computer systems a little too much, or was designed for information warware. Flickery pixely looks. Can fry anything computer-related by ease, also can draw info out of nearby terminals to figure out enemy weaknesses and thus boost damage.
A warframe with a large dinosaur-like tail. Grab it, whack it, smash it.
South American native theme (Aztec, Inca, Maya...) Maybe even a feathered dragon of their mythology? Possibly some kind of solar/fire powers, hidden knowledge, science. Visuals would be colorful and awesome at least.