To be honest, if Android had Zune I would have bought an Android device. Before I bought my phone (Omnia 7) I had never even seen the WP7 interface in person, it looked nice, but I had no clue how much I would like it. I'm now very glad that I chose WP7.
Branching out Zune into iOS and Android would be a bad idea, unless Windows Phone gains a monopoly. I think if more people were aware of the interface and the full extent of what WP has to offer, it'd be a much more viable idea.
Same applies to Office, why take away a key feature of WP?
Gmail on WP would be nice though, but I'm not sure what advantages it has over just adding a Gmail account to the Outlook client?