Alan is based here in East Anglia and has a particular love of the railways in this neck of the woods. Other members of the ATS team are based elsewhere in the UK and have concentrated on WCML/Trans-Pennine/Cross Country/ECML projects so who knows where it will be but I'd be very surprised if it wasn't in the UK. I'm rather hoping they can make the Stadler Flirts for TSW one day and do a route for them (WAML or GEML for example).
Assuming right this is the Alan Thomson from YouTube, they seem to take a particular liking to features and attention to detail, from what I’ve seen on their YouTube channel when they play/review dlc from TSW and TSC. sounds quite hopeful for some great standard route quality from initial impressions of them. I look forward in future to seeing what they have worked on.
I can maybe see them doing something with a TPE Class 68? Not 100% sure but I have a small feeling that a 68 may have an appearance.