I'm a very happy owner of an Edge 305 with HRM and speed/cadence sensor, and was happy to see the Garmin announcement of the new Edge 705. A little study of the manual reveals the 705 uses the same heart rate monitor and same speed/cadence sensor as does the 305. For we loyal Garmin customers (I own 3 different Garmin systems) who might want to move up from the 305 to the 705, however, it seems Garmin is not treating us well. You can't buy a "bare" 705 to use with the heart rate and speed/cadence sensors you already own. At a minimum, you have to buy the 705 with the heart rate monitor. I've verified this in email exchanges with Garmin customer service.
I would like to get the message to Garmin at a somewhat higher level: this is no way to treat your customers and protect their investment in your products. You should have an "upgrade" configuration of the 705. Even better would be a "trade up" program, giving some nominal trade-in value for a 305. But I guess that would be too much to hope for.