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You will soon be able to create any coin you like on top of Nxt. Nxt isn't designed to be a currency, it is designed to be a platform to be built on.
Nodecoin and Laksmhi are POW test coins that have been built upon Nxt to show it can be done. They are also protected from the traditional POW 51% attack by being secured by the Nxt POS blockchain.
See jl777's 'Coin creation Kit" or Come-from-Beyond's post in the Nxt Monetary System subforum. You will be soon be able to pick and choose any features you want for your coin (POW/POS/any inflation amount) and launch it on the Asset Exchange in a few clicks. Blackcoin could even be relaunched on the AE in a 1 for 1 swap.
Sorry if you think this is spam
Currently NXT,NEM,NXTL,NAS - all probably will have such exchange i don't see point in that in general.
Etherum will be also designing build in exchange but diffrent programing model will be included...
...To many features build in will slow down such currency and will cause bugs in security.
More features more possible bugs/exploits.