The Saikyo Line connects southern Saitama Prefecture with Akabane, Ikebukuro, Shinjuku, Shibuya and Osaki. While the Saikyo Line technically ends at Osaki Station, many trains on the Saikyo Line continue to run on the Rinkai Line from Osaki to Odaiba, before terminating at Shin-Kiba. Rolling stock 205 Series E233-7000 series TWR 70-000 series Sotetsu 12000 series
I'd be interested, though as with many of the lines around central Toyko it's going to feel very empty without all the AI. Another issue I can see is the need to get approval from both JR East (who own the Saikyo Line) and TWR (who own the Rinkai Line) It is a joint operation. One alternative option (avoiding TWR) may be to have through running the other way from Omiya on the Kawagoe Line to Kawagoe. That brings the length to around 53km and would be a contrast between the busy area around Shibuya and Shinjuku and the single track lines around Kawagoe. Stock wise I'd probably just stick with the E233 - but do it in both 'metro' and 'outer suburban' versions - apart from the colour the 'outer suburban' has toilets in some cars as well as 2 double deck green cars (First Class) in 10 car sets - That way you have something you can use on the parallel lines and expand the options for the player.
An additional thought, it may be an idea to do a version with a blue stripe for the Keihin-Tohoku line, that parallels between Akabane and Omiya and maybe include the other route between Akabane and Omiya - The Shonan-Shinjuku and Takasaki lines as a stretch goal. Even if the K-T trains are off limits for driving it's a quick and easy way to increase the busy-ness of the route
