I understand Round2 has quite an inventory of old kits that can be used for reference in restoring or modifying the old AMT and MPC tooling.
As far as Jo-Han subject matter, I doubt if many people under 60 would be interested in the '67-'68 Imperial, '57-'61 New Yorker, '62-'68 Chrysler 300, '55-'60 DeSoto, '55-61 Belvedere and Fury, the '58-61 Dodge, '56-'62 98 and Super 88, and '58-'62 Fleetwood.
I think the '63-'70 Coupe deVille might have a few candidates, and the '63 Olds Starfire, and '66-'67 Toronado. The '68-'72 442, '71-'76 Eldorado, and '69-'70 Road Runner and GTX could be tooled in hardtop and convertible variations. But it would probably make more sense for a model company to start from scratch since the Jo-Han models typically have molded-in exhaust and underhood components that today's modelers frown upon.