The legal information when starting the game shows an acknowledgement for Ouigo, despite Ouigo not being featured in any DTG DLC. I have no idea why it's in the legal bumph, but I expect that it has something to do with the general SNCF license - that said, I do wonder if Ouigo is or was planned for TS.
With DTG having new French owners and French routes / rollingstock now in the game it’s definitely a possibility we (may) eventually get Ouigo services for the game which would be nice and would offer some extra French railway diversity for the game.
Could just be one of the requirements of a license with SCNF perhaps? (I'm just guessing, i honestly don't know )
Ouigo services use TGV Duplex stock rebranded. Just recently they introduced a slower service using convention locos and stock https://fr.wikipedia.org/wiki/Ouigo There is a repaint pack for the TGV Duplex sets on Rail-Sim.de https://rail-sim.de/forum/filebase/entry/3899-tgv-thalys-pack-v7-1/
I would like to see something from the classic loco hauled/Corail era. Part of the Calais to Basel via Lille and Charleville route maybe. Found memories of the old 2000 Calais Maritime to Basel overnight service, grinding around the curves at O dark something while trying to doss on the plastic Corail seats (which admittedly were more comfortable than the hard red plastic part seats DB put in their UIC compartment stock).
SimExpress is making the Z 20500 units used on the RER network and the Nord Pas-de-Calais TER network. I am not aware of any RER routes, however. Fair enough - the speculation train can terminate here.