[PROJECT BRAINSTORM] What do you want in a Bitcoin client?

[Coincomm]

I am giving you a blank canvas here. If you were to make your own Bitcoin client, what would it have and do?

[flipperfish]

• Support for Brainwallet: Generate deterministic wallet from passphrase (choosen by user, entropy enforced by program).
• Support for different Keystores: So it will be easy to integrate smartcard or mobile phone
• Extensible for different blockchain-backends: Remote server, p2p-download or some newly developed method --> User can decide about trade-off between security and speed
• Multi-Platform: Ideally runs completely on virtual machine (like Java VM, Python Interpreter or .NET Runtime) without platform-specific compilation steps, etc.
• Open Source with *structured* code (SOLID, etc.).