I think the Freightliner 122 would be a nice, more traditional American truck design. That is their only other highway truck that fits into the kind of trucks in the TS games. Technically there is the older
M2 Class trucks as well, but they don't even show it on their main page anymore. I think they are in the process of replacing these trucks. They used to be called the Columbia and sat alongside the Cascadia. All named after their Pacific Northwest origins as a company.
For International, we are missing the RH Series truck, which is similar to the LT.
The last Western Star I would like is the classic
4900. I doubt it will come since Western Star seems to want to promote just their new line up of trucks.
Outside of Daimler NA, we are now missing anything new from PACCAR branded trucks like Kenworth and Peterbilt. I am willing to bet those will come within a year or so.