I agree with you on the modular aspect.
As for the size of the blockchain, i think that if nu is successful in becoming the first currency of the Internet, the blockchain is likely to get enormous.
So most of users (except shareholders) will not download it, we can speculate.
Is it a problem?
Well, no, if b&c can provide decentralized wallets, decentralized bank accounts in fact, using the multisig mechanism, we have a very robust solution to the blockchain cloating problem, whether for nubit, bitcoin or peercoin.