It is a step-up in the sense of looking at how casual audiences see the MU. The Avengers are the big team that's prime time. Being part of this team highlights her as Marvel's A-List premiere team, and shows Marvel values her now as a solo character who can carry her own ongoing series while still being popular enough to be on the Avengers. Like Iron Man, Captain America, Thor, Black Panther, etc.
And I feel Marvel wants us to associate her with these big names now because that's the plan for synergy with the MCU. It's all coming together. Like others said, Wanda and Vision are also exes so I don't think that's going to be a problem for Storm and Black Panther. And frankly, I still remember how snide some T'Challa fans were about Ororo back in the day so this is the perfect way for them to remember that this goddess is not going anywhere and she can outperform him anyday. T'Challa got his big boost from marrying her so there's a nice irony here.