The class 320 EMU built by BREL in York runs on all Cathcart circle services. This addon would bring more variety to the Cathcart circle
It might add Variety to the Cathcart Circle but it's not much. Realistically you'd get way more AI at Glasgow and Newton than you would player services on the Cathcart Circle. The only train that would really add anything significant would be the Class 380 - however that would be far better suited to another route, such as the Ayrshire Coast Line (where they run exclusively - excluding areas shared with other lines) or the Inverclyde Line (where they are one of the main traction types - and if you backdate it a few years, it would be the 380 and 314 running alongside.)
For the time period the route is set (pre-abellio) the only other units running services on the route were 380s