Yeah, that's the tricky problem with the situation of a mopup guy. My read is that they may eventually try and use him in higher leverage situations, but that they also want to keep him kinda stretched out in the event that a rotation spot opens up. So my long-term kinda strategy is to hope I have him as a SP with RP eligibility later in the summer, but I need to establish some kind of cutoff point, especially since he's a player / team I'm rooting for.
I think the rotation situation is fairly fluid: Kuhl is closer and closer to thin ice, and Brault is just holding the fort until Musgrove is ready. I expect Musgrove to be pretty solid in the NL, but I think one rotation spot will eventually be open without even accounting for inevitable injuries.
Problem is, they already turned to Brault as a fill-in, and I wouldn't be shocked if they just want Glasnow getting outs all season in MLB, and won't attempt anything like putting him back in the rotation right away. He's still just 24, so they can easily have him do bullpen duty all season, and revisit starting again next year. For now, I'm riding it out a bit in the hope that he might take one of those spots in June or July. It could behoove the Pirates to try it out once more anyways, since the rotation is already somewhat crowded, and Keller will at least be knocking at the door by spring training next year. Glasnow just has the tempting ceiling -- a fixed Glasnow paired with Taillon and Keller would give them a potentially great core, supplemented by useful guys like Williams and Musgrove. Who knows, Glasnow seems like a safe bet to remain an enigma, but I will say that he looks like an objectively different pitcher this year now that he more or less knows where the fastball is going.