Nimoy delivers the line, "Space, the final frontier...." in a teaser that is apparently meant to invoke the original spirit of space exploration in the 1960s.
Perhaps it should've been Pine delivering the line. Pine's voice juxtaposed with Kennedy and Armstrong would've bridged the gap between the 1960s TOS and today.
Further, probably every non-fan (that "casual movie-goer" the film needs to attract) who has ever heard those words before associate them with Kirk (OK, and Shatner).
So, using Pine could've continued the theme of the teaser that from the spirit and energy of the past, something new is under construction. And a young Jim Kirk is about to "boldly go," again.
Not that I'm upset with the teaser. Just saying that it actually may have been more appropriate to use Pine.