Sounds like you do not want to morph that pitch into a slider based on how I understand the two pitches. Maybe he can develop a distinct slider, but I don't think he should be doing much more besides continuing to refine what is working.
This is going to sound a bit conservative, but I don't think there's any need to rush him to AAA. If he puts up another couple starts like this, you won't have a choice, but 1) he has barely pitched above single A; 2) we're coming off the pandemic year; and 3) amidst the genuine hype we should be feeling, we shouldn't lose sight of the fact that a question about him is whether he'll maintain velocity. He's had the big spike and now with three solid strikes, seems to be maintaining it just fine, but this means he's doing well and you want to keep him doing well.
I think he's the 4th youngest pitcher in the entire league, which would surely also be true in AAA. There's plenty of time to let him earn his way into a AAA rotation and I don't think we need to be excessively cautious or anything, but I'd just let him face another 2-3 teams, see how the stuff is holding, etc., before going to that extra level. There's probably no reason to let creeping thoughts happen about a cup of coffee in MLB (surely we will be patient there, for a variety of rasons), but it's very doable to have another 3-4 weeks in Altoona, and then a strong batch of AAA games. If he dominates, he dominates, and I'm also of the mind that with a window you hope is opening (with Hayes), messing around too much with service time has diminishing returns, but we can cross that bridge when we get there.
For now, his next start is appointment viewing.