I hooked up the new B&G Zeus Touch 7" yesterday and so far it looks to be a worthwhile upgrade. The mounting bracket has the same hole spacing as my Lowrance HDS, and I had to change the power cable but everything else plugs in (sounder, NMEA2k, Radar Ethernet). The boat is still on the hard so I couldn't test the sounder, but it's picking up the sensor so it should work. I picked up heading and rudder info from my Raymarine ACU200 autopilot so I know the AP interface works over the NMEA2k, but could not pick up wind instrument data, so that's an NMEA2K/Seatalk issue on the Raymarine side for future investigation. I was also able to test radar and radar overlay on the charts so that's OK. Radar controls are identical to the Lowrance. I also tested using the Navionics chart chip I had been using on the Lowrance.
The user-interface is better/faster than the Lowrance, for example if you touch a tide station icon it instantly brings up a tide display with full graphic chart, and you can work with it or press "x" to close it. For comparison: The Lowrance would require you to step through 3 or 4 layers of menus, and scrolling through Lowrance menus requires a button push to move past each selection, then another to select one.
The touch interface is near-instant response and it's apparent this unit has a MUCH faster processer than the Lowrance HDS Gen 1. I'm seeing Lowrance HDS7 head units selling on eBay for $250+ so this $400 is definitely a worthwhile upgrade.