Now we know which actor will be found inside the pod when Season 2 picks up: Chris Wood.
[The following includes potential SPOILERS for Supergirl season 2.]
Supergirl was confident enough of a second season (which it got, along with a move to The CW) that it opted to end on a cliffhanger.
Wood (The Vampire Diaries) had previously been cast for an unknown role in Supergirl season 2, but at the show’s San Diego Comic-Con 2016 panel it was confirmed that his as-yet unknown character is indeed in the one in the Kryptonian pod in the season 1 finale.