First i've ever heard of it. I used a prototype 2X teleconverter with the 100-400 before the camera was even able to recognize that there was a teleconverter attached almost two years ago. It functioned properly then.
You are trying to make it easy on yourself by parceling this deal. Do the opposite and make it easy on the customer to purchase what they want to purchase. Break it up!
That eyecup will cover half of the rear LCD! Wouldn't it also permanently cover the eye sensor? The gent above is telling you to change the brightness of the EVF, not to set anything else differently. You can still view your photos with zero processing in the EVF.
His tune will change when there is sufficient stock of the camera. Until then he will harp that another camera (that is well stocked) is the best choice and everyone should buy it through his links to reputable dealers, from which he will get a small percentage.
I'm not knocking your decision milandro. Instead i've answered the OP's question, "I wonder if the 50-140 is worth the price if I want to use this for portrait and playing kids?"
I'd keep the X100T. The Xpro2 is a fantastic camera, one of the best i've ever used. But the form factor, size and as mentioned discreteness sets it apart from it's larger sibling.
Press the Menu/OK button for a few seconds. Your controls, including the drive button will unlock. It's a feature of many, if not all Fujifilm cameras.