There will be a quasi-decentralised-exchange for BTC. BTC will be implemented on the Crypto-Gateway using the NXT asset exchange. So you can deposit BTC and will receive BTC tokens, that you can sell for NXT on the asset exchange. Those tokens can be cashed out anytime! I will personally guarantee for the stored funds and will do the coldstorage.
Other currencies that will be added on launch: NAS, NHZ
Details can be found here: https://nxtforum.org/index.php?topic=1317.0
there is also InstantDEX which you can actually invest in on the exchange. Shares are trading at ~34NXT per share.
-bm