Sounds a bit like Cinema4D. I don't mind the modular approach so much, but that's not what Carrara is about (so far).
Also what would the cost be for this kind of approach? Would you be willing to pay Cinema4D prices after getting used to Carrara prices? I don't think Eovia/Daz/whoever would be willing to make such a big change unless the price goes up to cover more programming work (I think).

I'd suggest dumping the standard vs pro thing - upgrade Carrara Basics a bit and make Pro the main version. If the software is good enough you don't need to add the Pro label, theres no Maya Standard or Pro.