The two reason not to have grass -- slope and shade -- looks like one of them is there and the other is coming. I think it would be better to extend the groundcover over to encapsulate the steps. If you want the step sides to show, you just have to keep any plants trimmed back a few inches. It will be a pain but it's your call. I wouldn't plant anything between the steps.

Thank you! And because the tree's shade extends so, the pachysandra will grow consistent with the other side. Would you suggest any decorative pot planting on either side of the top step...or would that be bordering chachki?

I think pots of anything flanking the steps, up top, would be a negative, not a positive.

Thank you again. I'll post an 'after' soon.