Well, I have been rethinking this Insteon technology a bit.
It sounds more like they have a proprietary protocal which sends its information over the powerline which will talk only to other Insteon modules. It also has two plugin modules that transmit RF and "talk" to each other. If you plug these units into separate phases, this will couple those phases without a signal coupler/repeater in your breaker box.
One advantage of this RF is that you could place say and Insteon motion sensor (or other future products) that will transmit RF as well and have the system be able to talk to it without having to be wired into the powerline!
Also, if this new Insteon protocol is as robust and reliable as something like UPB, then it will be well worth it.
I guess it is to early to tell. If there is a computer based soluton/controller AND a software package such as Homeseer that was able to communicate with it, this could be a bridge between Insteon and your current X-10 systems. I wouldn't like this because my Ocelot would not be able to communicate with Insteon (without any computer). Unless of course if Applied Digital decided to create an Insteon compatible device as well.