I am pretty firmly in the keep him at SS camp for sort of three reasons.
First, obviously, if you have an offensive monster who can capably play short stop, you are really cooking in terms of an MVP candidate. Even if the hit tool only hovers around average, if you get average defense, plus speed, and plus plus power, it's just absurd.
Second, it's probably the most athletically demanding position, so the fact that he's already convincing a number of scouts that he's able to stay there is a good idea, and I think strategically also makes it likely that he could still end up at a fairly high value defensive position. Rumbunter addresses him in the Q&A they have up today, saying that he'll be the long term DH, and while that's not implausible, right now I think it's somewhat absurd. Maybe he shifts there eventually after he makes the big leagues, but he's going to be playing a position initially. He's still improving his game at SS and this will be a big year for determining it, but I would say that if SS won't work out, you see how he fares in CF first, then probably RF.
Third, a slight bit more of a stretch, but there is an important mitigating circumstance here, and that is Ke'Bryan Hayes. Even if Cruz only maxes out as hovering around average defensively at SS, he can be paired with an elite defender on the left side of the infield, which will help reinforce the rest of the value he gives you. If you start to think about Newman being more of a plus than average defender if he switches to 2B, then you are really in business. Lots of dominos still to fall, but Tucker could be a good option off the bench, and you also have Alemais as an elite defensive SS still around, to create an eventual scenario where Cruz is the regular SS but is sometimes rotated through the DH spot to keep him fresh.
We'll see how things unfold. As most of us should know, there is a danger to dreaming too much on completely unproven prospects. I think the Pirates find themselves in a pretty unique situation this upcoming year, with looking to assess the current crop of MLB young talent with a wave that is possibly on the horizon. Let's include Keller in with Reynolds and the others and set that aside: 2020 has the potential to dynamically change the near-term outlook for things, and it sort of hinges around three names IMO: Hayes, Cruz, and Oliva.
I think Hayes is a lock to play in MLB this season, and Oliva should be a good bet for at least a September cup of coffee, with Cruz perhaps even having an outside shot at that too. All three of these players have the potential to be above average contributors or greater, and they play three absolutely crucial positions. Between injuries, performance setbacks, and other questions separate from these three guys, a whole lot can change in a short period of time. But they will be the names, besides Keller in MLB, that I am keeping the closest eye on during the season, because simply put, if all three have very good seasons, continuing to build on the stock, then if we are looking at all of them as possibilities to start next February, we'll really be in a much different shape, especially if Cherington is able to churn a bit at the deadline and add a supplementary player or two.