I'm not a developer, but I wonder if any thought has been given to working with the open source OpenChange project, to enable Zimbra and Outlook to work together without the need for a MAPI connector. I see two benefits of the Zimbra community taking this on:
1. Obviously, a free and open source solution would greatly enhance the value of the Zimbra FOSS edition (and remove the burden of Zimbra having to maintain its own connector for the NE).
2. In general a transparent MAPI clone, with a large "constituency" of users and developers across multiple MTA implementations, seems likely to avoid issues that people have had with MAPI connectors in general. (I know that Zimbra's has worked for us in light testing, but I've also read of problems.)
Yet a search of the forums shows only a couple of incidental mentions of OpenChange. I realize that the Outlook connector is likely one of the drivers of NE sales; nevertheless, it seems Zimbra has been more than welcoming of developments in other areas where people have come up with FOSS alternatives to NE features (such as backup).