I am actually not really convinced by @JordanLee’s answer in the bitcointalk thread:
Theoretically it could be. However, exchange and stable currency are two completely different business models. It would complicate the protocol a great deal to accommodate both business models and increase the risk of an unexpected malfunction in the protocol.
Probably the best reason to separate them has to do with scalability. Creating two blockchains and two networks reduces blockchain size considerably and reduces the number of transactions and messages that need to be processed in each one.
There can be two separate blockchains, one BKC and one NBT, which are both secured using different staking processes but using the same NSR. Of course each NSR is eligible to stake on both chains at the same time, since they are different blockchains - NaS is our friend here.
Any NSR holder can always decide if one or both blockchains get synchronized and if staking is performed on none, one, or both chains. There is no scalability issue for pure NBT users or BKC users.
Both blockchains are different protocols, its only the same proof of stake that can be used on both chains. So any malfunction in one protocol won’t affect the other.
Where do I think wrong?
EDIT: Well not sure how to send NSR in above scenario, so its probably not working like this. I also assume that you spend a lot of thoughts on that, and probably would have preferred a single share solution if it wouldn’t suffer from those drawbacks.