That would be very cool!
If anyone would have the "guts" to do it, Moebius would be my guess.
Uh, surprising as it might seem, a '56 Imperial would have to be an all new tool--in real life, the Imperial was something like 7 inches longer than the Chrysler Saratoga, which is what the C300/300B were built from. On the Imperial Southhampton convertible/hardtop, all that added length in in the wheelbase and overall length, with the hardtop roof (convertible "greenhouse is the same basic length more or less) being the same as for standard Chrysler.
Agreed that the Imperial would make a cool, COOL model car kit, but somehow I doubt it will happen in styrene. Enterprising resin caster? Hmmmm?