They're too real. If they can keep their relationship good and keep rising up together, being good at what they do then I think they will be another power couple. They made a song together which explains how their relationship is and how they want to stay together Big Sean even says he may want to start a family with her. If they keep up their success then they shall be worthy of the title "Power Couple".
If they can make a relationship work business wise then there could be a chance for them. I feel it is very important for a couple to be able to grow as a team together. They make great music together and seem to have a genuine attraction. In one of Big Sean's songs "10 to 10" he claims to work really hard if they can balance work and play they seem like they'd be happy. The limelight should not affect them much if they can keep focused on each other and the truth between them.
A simple incident where two people (specifically celebrities) are (possibly) caught kissing does not mean there is going to be a marriage the next day. These kind of things happen everyday between celebrities. If anything, it is probably just a one time fling. More than likely, however, it is just a publicity stunt.
I have no idea who Big Sean and Ariana Grande are. A power couple would need to be two well known people who have influence. These two do not have either, so I do not see how they can be a power couple. People who have some celebrity are not enough to be a legitimate power couple.
While they are coming out to the world as a couple, they have stiff competition. On one side we have Kim and Kanye, then there is JayZ and Bey. Big Sean and Ariana are small potatoes in comparison. The music industry hasn't room for a number 3. Although it will be entertaining watching them try.