Why not?  Is it planned at any point?

N.B. There is a distinction to be made between assets (USD, Gold, BTC, etc) and stocks (MSFT, GOOGLE, etc).  For stocks, there should always be only one issuer.  However, for digital assets, you really do want to support multiple issuers because this gives you high availability, decentralisation, free market competition, etc.

Seriously, how do you think the one party who is allowed to be the BTC/NXT gateway will price his/her services?  With no competition the NXT exchange, as a whole, could very likely suffer from monopolies on assets like BTC, USD and gold.

That's my prophecy.