I agree. I only put Scott in the regular lineup because I believe he is much more likely to be kept on the NHL roster with everyone healthy than Ellis, but I agree that we'll probably see them alternating.
I think it really depends on what happens with Grigorenko and what Gerbe's injury status is, but I wouldn't be shocked. If Grigorenko sticks and everyone (including Gerbe) is healthy, they'd only be able to keep three of Brennan, Weber, McCormick, Scott, and Ellis. It's still to be seen which of the forwards on that list are highest in the pecking order, so it's tough to speculate.
edit: I know Zip floated this idea as well, but I think Brennan should be in the lineup as the 7th defenseman on a lot of nights while Gerbe is out. I think he has the potential to impact the game a lot more than Scott or Ellis with his ability to get a big shot off from the point on the power play. Rotating other wingers at that 4th line left wing spot wouldn't be a big issue on nights when Brennan is in the lineup.