I was biking by there tonight and i got up close to the piers in question. The wrap wasn't up all the way on the scaffold yet, so I was able to see the piers and a bit of the setup going on inside. On the 3 piers that are getting the scaffold, there appears to be an issue with moisture ingress into the concrete. The concrete, or at least the outer layer, is responding poorly to the recent rains we've had, and there is more dark staining than on the 'normal' piers, as well as a noticeable superficial cracking/crazing pattern. This pattern looks to be superficial, the kind of random lines one sees sometimes in concrete patches done with lightweight cement or in stucco scratchcoats. the cracks are all very small, revealed mostly by the excess moisture in the, as opposed to the dry areas around them. it's like a mess of wet cracks in dry cement.
I'm not super knowledgeable on the mechanics of concrete, especially stuff that's intended to be weather-exposed like this, but it looks to me like whatever finish layer got applied to the three piers getting scaffolded was too porous or otherwise not prepared properly, and is now aging rapidly due to moisture exposure. Like I said, it looks like the same cracking you see in porous/lightweight cement fills and patches in sidewalks and the like; and if I understand correctly, these piers were cast and then surfaced with a finish 'layer' or 'coat' of cement to give a consistent look.
This is all just my theory based on what I saw tonight. I don't know enough about concrete finishing to know for certain. as for how this affects opening; IDK. The issue can't be structural, that would have been picked up by now, especially given the viaduct segments the piers support have already been replaced, and I'm sure things were re-checked when that happened. There was a small electrical box and some wire hanging on one pier; I didn't think much of it and it wasn't labelled. any guesses?
Assuming the cast-in-place cores of the piers are structurally sound, and it's just a surfacing issue that can be resolved entirely from beneath the tracks, I'm betting the line opening shouldn't be delayed by this issue. That is assuming that there's nothing else wrong here, of course. hoping ofr hte best!
Anyways, here's a couple pictures I got using my bike light as a flash. the first two are of the scaffolded piers, the last is a photo of a normal pier to compare, given the bad camerawork. This stuff is a lot more visible in person.