A future U.K. route will be somewhere in Britain and that’s about as much information as you can take from that.
Hopefully, another London Underground route like Piccadilly, Central, Metropolitan or the Northern line.
Seeing as this is off topic and nothing to do with TSW I am going to walk along the cliff and say, late, over-budget, and unlikely to be completed in full.
It's definitely going to be on Planet earth as far as I'm aware. Though seriously, just wait and see. We have nothing as of right now.
Stourbridge Junction to Town, £24.99 with the Parry People Mover as a separate DLC at £11.99. The main achievement will be completing six consecutive round trips without blowing your brains out.
It will be the Watford Junction - St Albans Abbey line - perfectly modelled to the extent that no trains are running, there's a replacement bus service so the DLC is actually a 10% discount voucher for OMSI.
people say U.K. mistakenly when they mean Britain or England most often, so not very clear if DTG ever meant to include NI as considerations for that category. Unless they ever make a route for it beforehand, I wouldn’t expect it as potential. technically the U.K. name is the overseas territory as well and I don’t think they’re potential neither.
Sheffield to Hull line, modern day. Only because I know a fair bit (such as sounds, the trains, and what some of the stations actually look like), and can be nitpicky
I’m going have a bet for the next British route to be Manchester to Liverpool. People often bet their local route as the next (mine being Durham Coast Line) I know it was done in TSC but can’t see it for a while at least for TSW.
I think rivet might be making west Highland line. Oh gawd. I'd love to see my local line built by Just Trains, Skyhook or dtg. (Ayshire Coast (Ayr to Glasgow Central & Ardrossan Harbour & Largs to Glasgow Central)/Glasgow Southwestern Line (Kilmarnock-Carlisle/Kilmarnock-Glasgow Central))
Metropolitan Line is the known one because it's a TSC Just Trains route. If remade for TSW 4 think of it as Blackpool to Ormskirk via Preston meeting the Bakerloo line.