The issue is that there's only 1 spot between him and POJ and POJ's not playing badly enough to lose out on the role. They'll have D injuries sooner than later and Smith will come back up, but I do want to see him as soon as possible.
The interesting thing to watch is to see if POJ's trade market can develop at all. He hasn't played amazingly well to increase his value, but he's also showing that he can play a regular role in the NHL. It's still early, but more competent games in the NHL will ease the "we don't know if he's NHL ready and we'll have to waive him if he's not" concerns that other teams have.
You hope he goes from that Juolevi/Pouliot tier (former top prospect with waiver eligibility and questionable NHL talent) to the Siegenthaler/Pettersson tier (young NHL D stuck in a numbers game), it's just a question of how long that will take with him.