The trailer shows Rey and her friends, but is that who he’s referring to?
There’s another sound byte earlier in the trailer from the Emperor about how he’s waited for them to come together.
If I were a betting man, I’d have to think the Emperor is talking about Rey and Kylo Ren.
This scene appears to take place during the climactic massive battle between the First Order and Resistance, as evidenced by the copious amounts of lightning and blue-gray tint to the picture.