develop webmail clint with ajax/extJS based on a public emai

We currently use horde webmail, but dont really like the interface, so the project is about to create a full featured webmail client with extJS javscript RIA framework for UI and as php frramework to use horde, - use kohana php framework OR directly use horde (we like the features of horde, just not the UI) - implement the UI in extJS (not just a horde skin, its a total new Javscript/ajax UI and need to support all comon features of horde) - some custom api integrations to 3rd party messaging servies - use our python appserver as data store, NOT use mysql (we provide the api) - you can use modules like tinymce as email/html editor (for example for email composer,...)