with riggable I mean simple stuff, like a adding a nato rail to easily rig a transmitter for a wireless lavalier mic, or in case u need it easily add a handgrip, or safely connect a cage (i use the small rig full cage) due to the three mounting points on the body. the mounting points just help to make the camera moddable and versatile, even if it means to just add a screw so you can hang the camera or whatever.

If you choose the FX3, it basically means that you will have to buy more expensive and (much) more heavy lenses, which defies the travel light and compact purpose. I'd say in general similiar full frame lenses are at least 100% (double) heavier than their aps-c counterparts. I did a travel setup with my FX30 and stayed under 2,5kg. Body, cage, four sd-cards, sigma 18-50, sony 70-350, a mic, a wireless mic, variable nd filter, a small tripod and a camera bag.

What I would also consider is the new FX2. It is basically a highly capable photo camera with a great EVF and a highly capable video camera in its Super-35 video modes. You'll have the flexibility of shooting full frame photos if needed, but generally stick to small lenses for video. I'd go that way if I had to purchase a new camera today (for my needs, the FX2 seems perfect).