Yeah, seems like an unfinished feature... I could understand it if I got comment updates on files I follow, downloaded or I've uploaded myself but it seems absolutely unnecessary to have for every single update on the website! It also most be quite a drain on server bandwidth having to push these to every single user every time somebody comments on a file.
It isn't scheduled, at least publicly, but I would be very surprised if Carenado didn't bring their ATRs into the sim at some point.
The one that is probably gonna be released first is the CRJ series by Aerosoft. They say that they want to get it out before christmas (Probably to get some money on the christmas sale ) But you can expect it in the next year. Recently they announced the price aswell. The base package will cost €42 (plus local VAT) and contain the CRJ 550/700. Then if you want more you can purchase the 900/1000 model for an extra €16.75 (plus local VAT).
PMDG are also working on a 737-800 but that got delayed to Q3 2021 or even later. This is due to the incomplete SDK. But their aircraft are at really high quality though so if you want that quality you'll have to wait . No price yet at the time of writing.
There are also rumors that FSLabs are making an A320 but that is not confirmed.
You also have DC Designs who are bringing the Concorde if you want to fly supersonic.
This is just the beginning of MSFS2020. Hope you have something to look forward to now
None of them are turbo props though which OPs question was about ?
Now I can only assume that Carenado will bring their ATRs, Fokker 50 etc. to the sim! It'll probably be some time before that happens though, but hopefully sooner than later ?