I think he'll always be a third line centre, with the ability to play second line minutes if needed on a short-time basis.
I mentioned this in another thread a few weeks back, but the thing with Eller is that he doesn't do anything exceptional. He's not a goal scorer, a play maker, a hard hitter or shutdown guy. He's not a strong faceoff player, especially speedy, extra gritty or a fighter. He does some things well, but nothing that makes him stand out.