there was no contradiction. it's a common trait of omegas to evolve past the human form as they ascend toward their full potential. elixir, a teenager, has already shown some form of self-alteration due to his powers, though he hasn't quite hit the pinnacle yet. where's that a contradiction?
here's how the other omegas did it.
jean encounters the phoenix force while dying of radiation poisoning, or with the retcon she could just be transcending to a higher state of being. who knows the exact specs at this point? truth is, though, that radiation was eating her body. very traumatic, very easily excused as the onset of her 'omega transformation.'
bobby has his body turned from that of a human body to that of a puddle by mikhail 'i warp all matter and energy how i please' rasputin. rasputin reformed him to living ice. on top of that, there was the entire emma frost incident which exposed the depths of his potential that he hadn't been using. in essence, he didn't come into this power on his own.
kid omega died, and courtesy of his mutation and some Kick, he went through some variety of metamorphosis that made him an unstable form of energy. he only came back to animation because of the phoenix force's activity on earth. traumatic event leads to his "ascent," ungodly power leads to his return to life in his new form. pretty standard.
elixir, a kid with healing powers, saves himself from death by using his powers on himself. it's not really a high-level trauma, considering it healed instinctively, but he did turn all pretty and shiny. consider it a lesser form of evolution if you will, but there are tons of reasons why he hasn't hit that point yet. on top of that, he's a confirmed omega.
jubilee's had decades of history to show some sort of omega potential, and she hasn't. on top of that, no one's come out and said "jubilee's a mutant with omega-level potential to create colorful explosions." i just don't understand how you trying fruitlessly to discredit what i've said would at all strengthen the 'jubilee could be omega' case.