The next cheap car could be the Mustang Dark Horse. The blue color on the submarine would work well in this.
For 1:10 cars, I’d love to see an Aston Martin Valkyrie in Dark Green Metallic or Dark Turquoise Metallic.
As far as the flagship goes, they could offer a RC tellehandler. Four motors and a single hub would be enough for basic functions, especially if run through a gearbox. Boom extend, boom lift, fork tilt, drive, steer, and stabilizers could all be done with four motors. A tellehandler wouldn’t have that much bodywork, so I think this could be done with 2300 pieces.
I think a backhoe could be done for 2300 pieces as well. 8455 only had 704 pieces.