Well the original E-body Challenger was essentially based on a shortened B-body chassis...
But I have to agree that in the grand scheme of things that it probably wouldn't be a practical idea, all things considered.
As far as Pontiac is concerned, it seems to have been going thru a major identity crisis of epic proportions for the last few years, and it'll continue this way as long as Uncle Bob (Lutz) and the rest of the powers-that-be at GM continue to hamstring it. There is
tremendous demand for a new Firebird and it would be undoubtedly a huge hit... but it seems like anytime such an idea is brought up, Uncle Bob puts his hands over his ears and yells "LALALALALALALA!!!!!!" (picture Eddie Murphy's character in Beverly Hills Cop in that one locker room scene and you get the idea).