I think this would be a great route to have in TSW. Tay bridge and forth bridge, the line up to Aberdeen and Dundee including the branch from Ladybank to Perth.
Edinburgh to Markinch already exists so at best you'll get a route starting at Markinch and heading northbound.
Fife Circle should've gone to Perth/Dundee rather than end at Markinch. We got the circle, yes, but ending a run at Markinch when Perth and Dundee aren't much futher is annoying.