Was potentially planned, never happened. With DTG not touching US freight and not wanting to do vintage stuff due to research, the only way the MILW would ever come to TSW is if Milepost Simulations (Who is making a MILW route right now for TSC) makes one for TSW in the FAR future.
Along with the Milwaukee Road Boxcab, Bi-Polar, and Little Joe electric locomotives, I'd also love to see some 1960s-70s-era MR diesel power; maybe an SD45, SD40, E8/E9A/B, GP7/GP9, F7A/B, FM H-10-44, and FM Erie-Built A/B units (love the livery on MR's FM passenger units). The Hiawatha passenger train (with interior views) should be included, along with MR freight and cabooses (also with interiors).
I’d absolutely love to see this. Vintage electric locos are a particular passion of mine and the Milwaukee Road’s so interesting precisely because they were such an unusual railroad. I particularly like the simple charm of the boxcabs but their other locos like the Little Joes, the Quills, or the Bipolars would be more than appreciated as well.
I'd actually prefer to see electric motors of this time period on a New Haven Railroad route. The New Haven's EF and EP-series motors were pretty similar if not identical to the units the MILW was fielding. Something with maybe a set of Washboard EMU's, an EP5, and EF4 running between New Haven and Stamford would be fantastic.
Those exists in Train simulator classic as a downloadable content for Northeast Corridor New York New Haven. If TSW4/5 wanted those trains the ideal solution is making them present day and then DLC the past locos like the NH RR Stock and Amtrak E60s in TSC
Last I checked, only the EF4 is available for TSC. Besides, it would look awkward having vintage stock run on a modern route. The UK and Germany both have period-routes from various decades. There's no reason why we couldn't have a New Haven route set in the 1960's; the route for the most part is the same as today, aside from a few different stations and routings (Bridgeport for example). We already have two legs of the Corridor set in present day, there'd be no harm in having a PRR or New Haven-era leg of it.