I came upon three aircraft that might be useful additions to the game, two from Beriev and one from Sukhoi.
The Beriev BE-30/32 was a STOL aircraft designed directly for Aeroflot in the 1960s, to compete with the LET-410 and the AN-28, though it never reached high levels of production: https://en.wikipedia.org/wiki/Beriev_Be-200
The Beriev BE-200 is primarily an amphibious aircraft, but they have marketed a 72 passenger medium-haul aircraft starting in the mid 2000s: https://en.wikipedia.org/wiki/Beriev_Be-200
The Sukhoi SU-80 is a short-to-medium haul STOL aircraft introduced in the early 2000s: https://en.wikipedia.org/wiki/Sukhoi_Su-80
None are major variants, but they could be fun things to add for some variety, particularly in the late game settings.
Another that might be introduced is the GippsAero GA8 Airvan, a competitor to various Cessna products: https://en.wikipedia.org/wiki/GippsAero_GA8_Airvan
I also just came across the Miles Aerovan, a STOL aircraft operated from 1945 and produced in the UK: https://en.wikipedia.org/wiki/Miles_Aerovan
If you find a more official source of information than Wikipedia, with all the needed data, they will eventually added to the game.
Sure.
Miles Aerovan: http://all-aero.com/index.php/home2/6854-miles-m57-aerovan (everything else is from print sources and doesn't seem to be available online)
GippsAero GA8 Airvan: http://www.flugzeuginfo.net/acdata_php/acdata_ga8_en.php
Beriev BE-200: http://www.flugzeuginfo.net/acdata_php/acdata_be200_en.php
Beriev BE-30/32: http://www.flugzeuginfo.net/acdata_php/acdata_be32_en.php
Sukhoi SU-80: https://www.aerospace-technology.com/projects/sukhoisu-80/
And while I'm at it, starting in 2020 Cessna has a new aircraft, the Skycourier: http://cessna.txtav.com/en/turboprop/skycourier