[Pasha Paterson]

IIRC, each time SRS has used a paid mod, there's been a deal with the mod authors to offer that mod at a reduced price during the season. So it does happen on occasion. However, one of the fundamental philosophies of SRS is to keep it accessible to all players (hence why they don't require resource-intensive mods like CSP and Sol, for example), so use of paid mods is likewise kept at a minimum.

That said, yes, I'd love to see a series with the URD DTM cars.

But as Donnchadh has pointed out, RaceRoom is the official sim of DTM, and those cars are also excellent. If you are looking for an excuse to get more mileage (pun very much intended) out of RaceRoom, that series gives you a strong one.