The Shadow will be next. Girls: Rouge, Sticks, Lanolin, Neera, Nicole, and Sonia.
Silver will happen a bit later. Girls: Blaze, Gold, and Galaxina.
There is an older Shadow VN available that does not include the Nicole & Sonia routes nor the passion & epilogue endings: Shadow Ultimate Love "A Sonic Visual Novel" by Galestar01 -- Fur Affinity [dot] net