For a route suggestion we need more east coast mainline say from York to Newcastle with the Scarborough branch line
York to Newcastle is 80 odd miles so you're not going to get Scarborough as well. And if we do get another section of the ECML, let's have it in a different era - late 70's or early 80's with Deltics and Paxman HST's (along with the rest) working side by side.
I would love a 70s or 80s route with an original HST and a Deltic so much. A section with a 91 would be nice, but I'd like that on the current section we have now in its LNER design, along with a Grand Central 221 and Hull Trains 802 to add more variety.
Deltics are a must-have loco for either a 1960s-80s ECML or a modern Deltic railtour pack. A Class 37 or 47 for freight services should be included for the 1960s-80s route.
An extension to Leeds and York would be good, I know they're only two shortish sections but perhaps it could include the Leeds to York part of the triangle too, bung in a Class 91 and Mk4s and it would bring the ECML to life. Though obviously my no.1 would be Kings Cross to Peterborough because of the choice between metro, slow, semi-fast and express services and the amount of rolling stock that's already available for it. Edit: Or any section in the late 1970s with HSTs and Deltics.