Disclaimer, not a dev, info might be gappy or misremembered:
FS9, FSX, and MSFS have for ever and always had essentially no way to realistically implement proper turboprop simulation due to core sim limitations, which I'm sure you might know. In recent years BS and a few other developers have managed to squeeze somewhat realistic behaviour out of the platform despite its faults, but still it's only ever been possible to properly recreate turboprop physics by running the addon's physics outside the sim which is rare (Majestic is the only one I know to have done it).
Nick is a magician, but even so there's only so much that can be done in recreating a turboprop within MSFS, at least up until now. SU6 included a lot of turbine simulation improvements in its change log, hopefully this will translate to an easier life for devs and a more faithful recreation for us consumers. It's all hope for now though, I haven't seen any devs comment on it yet and it wouldn't be very surprising to find out that the changes hasn't helped all that much, but my fingers are very much crossed!
Edit: Again, with no specific knowledge, it's also possible that the SU6 improvements could be great for a ground-up project, but require a complete rework of existing products. Just speculation.
