Does the world need another cryptocurrency exchange?

[wolfgang42]

I know there's a whole slew of cryptocurrency exchanges out there, but I'm thinking of creating another one. Before I spend time on this, though, I want to make sure that the need exists.

Rationale
There are many existing cryptocurrency exchanges. Most of them suffer from some number of the following problems:

• They do not handle accounting data properly, for instance:
  • using floats (which may be rounded in strange ways) to represent quantities of currency
  • not using transactions in the database (which can allow money to be "double-sent")
  • storing balances rather than transaction history (again, this makes it difficult to keep track of money)
• They may have security vulnerabilities, and cannot be audited because the source is unavailable
• They provide no API for automated trading
• They support only one type of order (such as market orders or limit orders)

Design
To minimize attackable surface area, the exchange is split into two parts.
Backend
API server; handles database, accounting, currency transactions, etc

• Backend is open source; this means it can be audited for security
• Written in Python for readability
• Uses solid and well-tested software & libraries:
  • Flask
  • SQLAlchemy
  • Database: PostgreSQL
  • Web server: Apache, Nginx or Hiawatha (depending on configuration and performance--I need to do more testing on this)
  • Offsite backups: tarsnap
• Modular component system
  • Because the backend is separated from the user interface (frontend), there is only one way (the API) to attack the system; the complex user interface code is separate and can access the accounts *only* through the API server
  • Each subsystem is separated out into easily auditable modules with well-defined boundaries
  • Each currency is defined in a separate plugin; additional currencies can easily be added as needed.
• Append-only database: Trades & transactions are stored in the database forever. Account balances and transaction statuses are calculated from the full transaction history, so money cannot be "lost"--it always has to have come from somewhere. This is standard double-entry accounting, and the principle behind the Bitcoin blockchain.
• Decimal data types (rather than floats) are used everywhere for tracking money, to prevent rounding errors

Frontend
Website, user interface; connects to API server to perform actions

• Stateless: authentication data is stored in the user's browser and passed directly to the backend; it is never stored.

Features

• Multiple order types: Market orders, limit orders, and stop orders, with arbitrary cancellation dates.
• Simple but powerful user interface
• RESTful JSON API for computerized trading (also used by frontend, so it's full-featured and well-tested!)
• WebSocket interface for real-time updates

As you can see, I've given this a lot of thought. I have experience with all of the above technologies, and can easily build this system. However, before I spend the time to build this system, I want to know:

• Would you use this exchange if I built it?
• What volume of transactions (number and size) would you expect to perform in a given time period?
• Which currencies would you trade?

If you have any questions, please ask. I want to be as open as possible with this project.