(without reading the whole thread)
Of course it is viable. For 90% of jobs (sticks handheld shoulder) it is an excellent camera delivering a very solid image and AF where needed.
What more does one want?
Viable? as a daily rate rental/billable item.. surely the FX6 ate that a bit.
Viable? as a modern production tool. Well the mass is a downer on a gimbal.
Personally Im all about low mass so Id take the FX6.. but that is for my uses.
I guess I mean "viable" in adding the FX9 to the FX6 as an A cam - so running the 2X cams as a pair - like you mentioned - FX6 would be the gimbal cam and FX9 would be the main workhorse run'n'gun cam.
I had reservations about the FX9 when it first released around the same time as the C500 MKII etc but I used to own a Red Gemini and an FS7 II for the last 2-3 years and so I started to feel tempted by upgrading the FS7 to the FX9 when it was released.
So around 6 mths back -after evaluating what I actually need on jobs going forward as owner/op I decided to sell the FS7 and the Red to go either Canon or Sony for a 2x CAM setup and decided on the FX9 as I was used to the FS7 previously.
Then the FX6 was announced so i jumped on that first and now I'm looking to get either the FX9 or possibly go the other way on a FX3 as a 2nd cam but that is why I'm asking... is it viable to go for an FX9 anymore since the FX6 / FX3 have been released?
I see a nicer / sharper image on the FX9 and as mentioned it seems like a "thicker" image but it also seems like we've turned a corner already with the FX6 / FX3 released and maybe the FX9 needs an update already...??