I mean, I don't really count on her being playable either, but if this mention of both Black Tar and Uncontrollable does have some truth to it, there should at the very least be a bit more than just a boss fight. After all, from a sheer moveset standpoint, Elma would be pretty easy to adapt to 1's battle system. Either way, I just hope that they blindly force Rex into this, (because there's apparently also something involving him, urgh) and leave our colonel out.
Dread it. Run from it. Rex always comes.