Building an exchange/bank on the NEM chain

#1
 I'm still trying to wrap my head around NEM, but I've been wanting to pursue a concept of a semi-decentralized cryptocurrency exchange similar to Lykke with a built in crowdfunding platform/custom securities exchange. 

 After reading about NEM a bit, I am thinking it is a better choice than using the bitcoin blockchain as in the case of Lykke, or creating a native cryptocurrency like Bitshares. 

   Can anyone who has a thorough technical understanding of NEM offer their opinion or advice? 

Would it make any sense to use one or several private blockchains for managing trading and deposits? What I want is to get the speed of a centralized exchange with the security of deposits existing on the blockchain, and I think lykke does a good job of this, but it seems that NEM might be a better choice.

 Another question I have is regarding multi sig transactions. The most obvious use of this feature to me would be trustless escrow. What would be other applications? Could it be used to issue shares with approval of a board required to avoid panic selling or dumping? 

Just hoping for some help with brainstorming/integrating with NEM.

#2

If anything, I think that it is suitable for mijin® rather than NEM.
Mijin is part of the contents like the question is implemented.
Whether future functions will be provided from mijin® to NEM also depends on whether NEM’s goal is to be developed or not.

For mijin®, please click here.

Also please refer to the ICO project which used mijin® now.

We hope for your reference.