1) No, when used from the TV, using the PC source, the Beomaster looks and behave like the Beomedia. This is a disappointment I have to admint. You can download the Beomedia user guide on this site to see how it works.
It is far from being as nice as the BS5, but you have added features, such as Photo, Web, Video.
2) No the wheel on the Beo5 is only for the volume. The Beo5 will not bring anything more than the Beo4. Another dissapointement as well. That said, if you have the Beo5 config tool and A LOT of patience, you could reprogram it to use the wheel as a navigation wheel.
Regarding future upgrade. I would buy a product for what it does now and not trust any rumour about what it could/would/should do in the future.
For the moment B&O has promised upgrades, but did not say they will bring new features.