Male pregnancy is included in the game code (and, mind you, is unlockable with the use of mods) so there is possibility that alien abductions, that will conclude in impregnating the abducted victim, will be added in an expansion pack or otherwise. That said, not all hope is gone.
In my opinion, aliens along with alien abductions should've been added in the base game, but I understand EA's reasons, for the base game in vanilla form weighs over 6GB.
Edit: My apologies for going off-topic.