My proposal is a Class 730 Aventra for the WCML South line: London Euston - Milton Keynes. This addition would greatly diversify the line as the 730 slowly replaces the 350.
This would probably be made possible by a remaster/update to BCC as it's current state might not be suitable for them.
On RTT the class 730 cross city services are still listed as being pathed as class 323, so they likely match rather than exceed performance for now. There are a number of opportunities for enhancement/extension of the route though.
That would be incredible for improved layering and a greater variety of trains to add to the already incredible fleet
