Inspired by the Class 460 Gatwick Express, which was released many years ago (even though the Class 460 has now been converted into another EMU) my suggestion is a Coradia Juniper EMU Pack containing the rest of the Juniper family, the Class 334 and Class 458. It wouldn't even need to be as a pack, both units could be released separately. Class 334 Introduced in 2001-02, these units operate in the Glasgow area for Scotrail. Routes would be: WCML North - Glasgow Central (Low Level) - Motherwell/Coatbridge/Lanark/Carstairs Glasgow Suburban Northwest - electrified routes out of Springburn, Bellgrove, Glasgow Queen Street (Low Level) and Exhibition Centre Could either be provided in SPT livery or in the Scotrail Saltire livery. Class 458 These units were introduced around 2001 as well and operate for South West Trains in Surrey, Berkshire, the London area and have operated in Hampshire. Possible routes: Portsmouth Direct Line (original): Ascot to Guildford, London (from Woking) to Alton, London (from Ascot) to Farnham Portsmouth Direct Line: London Waterloo to Portsmouth - Waterloo to Weybridge, Waterloo to Guildford via Woking and Alton (from Woking) to London Waterloo Livery could be the original SWT or the later Blue SWT colours and both 4 and 5 car versions could be included.
There are plenty of routes you can use them on, I am surprised no-one has made them yet. Not even Just Trains or Armstrong Powerhouse have had a go yet.