Apparently the teaser shows a glimpse of the Enterprise under construction. So, if the very early days of the ship are shown, it may be that we see her first captain, too.
If it's April, then how does he fit into the story? Pike has a connection to Spock. Spock has a connection to Kirk. April has a connection to whom? Pike? Was Pike his first officer? Is that important to the story? How? Do we need to know that? Why? What's to be gained from seeing April? To that end, if the story works better with Pike as the first captain of the Enterprise, fine.
Further, why admit Pike is in it, and cryptically cast April as "Federation Captain"? The "Federation Captain" could even be the commander a vessel seen for a while in old Spock's time, for all we know.