I don't know why a pre-X2 project you created would open with FX in the ProChannel. I do think that is a bug.
As for using FX in the Pro Channel, it's pretty awesome. You can add FX to the Pro Channel by inserting an FX Chain module, or by dragging and dropping from the browser.
There are a number of reasons to do this.
1. Added gain structure
2. Added ability to control FX settings using Quick Groups- once you create buttons/knobs for the FX chain where you added the plugin you can control the same parameter on the same plugin in multiple tracks at the same time. You can already do this with the Pro Channel EQ, for instance, to add High Pass filters to all tracks at once by selecting all tracks, holding CTRL and enabling the Pro Channel to all, then (still holding CTRL) go to one of the tracks and turn on the high pass filter, grab the frequency and roll it up. Now this kind of control is available for all plugins from any manufacturer through the FX Chains in the Pro Channel!
3. Desired signal flow- now PC modules are not stuck before or after the FX bin, but FX can now be routed as desired
I'm in an internal debate on when/where/if I will use the normal FX bin in the future.
The Bypass All and Bypass All of this Type for the regular FX bins are helpful, and seeing plugins for all tracks at once when looking at the console view can be helpful too, but the quick grouping and routing make the Pro Channel bin a winner in many situations.
Peace,
Tunes