I'm sure we can all agree that the freight on UK routes has been somewhat lacking I.E more or less anything we have, besides the 66 and 37, is in a heritage railway or has been scrapped and the class 60 provides freight onto TVL and can be put in an EWS livery, maybe in future GBRF too for layers onto more modern routes. Class 60 (tug): The Class 60 is a Co-Co (2 sets of 6 wheel bogies of which all wheels are powered) Diesel Electric locomotive designed for heavy freight runs. They were built by Brush (you may recognise this name from Loughborough on MML) from 1989-1993 and began to enter service in late 1990 a total of exactly 100 were built of which 29 are in service, 66 are in storage, 3 are in preservation and 2 have been scrapped. They have a top speed of just 60 mph however they have been known to have better performance than the 66. I don't know much about freight so this won't be the most detailed suggestion but it doesn't really matter because the dev's (hopefully) do their research. CONCLUSION: This suggestion would be a successful idea as class 60s would be able to layer onto many routes as a freight loco but would provide more gameplay and a something brand new to TVL (based on the time period its set in)
The issue is that as you say they were introduced in the early 90s but TVL is set in 1989. I think a 56 would be a much preferable DLC as it could provide layers on both MML and NTP as well.
A 56 would be good but I think it would be much more interesting with a modern loco like the 60 because it creates variety along the route (I only recently found out the class 60 was built in the late 1980s I thought it was brand new)
That one's of personal opinion where I think a 56 would be better but the fact still stands the 60s weren't about when TVL is set. It would be like putting a 345 on GWE.