I think the consensus involves roughly two notions:
- PVC has a rather low HDT, or Heat Deflection Temperature. With plastics it isn't just about at what temperature they go noticeably soft, but at what temperature range are they unable to maintain their shape under sustained load.
- Honestly, I don't think anyone here knows how much heat your proposed system will generate, and whether or not it'll get up to ~50C, which is the lower bounds of the the HDT range for PVC.
That being said, I don't think PVC is the right material. It is somewhat unique among plastics for having a very low HDT, and is famous for deforming under pressure and modest heat. It is almost never used for applications above "room temperature", at least not where there aren't litres of water flowing through them to carry away the heat. The fact that PVC is acceptable for high efficiency furnace exhausts speaks to how little waste heat condensing furnaces make. Not to mention that it took years for building code to allow for PVC exhausts (in my locale, anyway) because it wasn't a sure thing that they would hold up to the modest heat and corrosive environment.
If you are going to be watching the thermometer instead of the work then the tool won't be as useful. And if one day you forget you are going to deflect the drum well out of round and it'll be near impossible to make round again.
I would suggest ABS if you are hell-bent on using plastic. I'd skip the fancy 3D printed insert and go for wood circles to drive it, or something equally as rigid.
But, honestly, the traditional material for sanding drums is wood and there is a reason for that.
- Wood can be resurfaced round again, for years and years
- Forgiving surface when you push a bit too hard
- Durable enough that you won't have to be dainty with it, and can get much hotter than any plastic if that happens by mistake
So, while I don't empirically know how this material will work in this application, if I put on my materials sciences hat it doesn't sound like the right material. And if I look to the years of tradition for sanding tools I don't see many (or any?) examples of any sort of plastic being used like this, for either home-made or commercial products.