I'll mainly use it for taking candid photos of my 3 year old son, and in indoor. So the lighting will be poor most of the time and as the background will really not be that far way from the subject, I need a large aperture lens for background separation. 35mm f/1.4 on APS-C is the only sweet spot for me, not too wide, 50mm equivalent, good bokeh, fantastic IQ. The only problem is AF speed. It hunts and misses a lot. I'm already using this lens with my XE1 I bought 3 years ago (didn't have a kid back then, had no idea how fast they move). I agree with jlmphotos, it is frustrating to miss their shots, the keeper ones are decreasing as the kid is growing and moving even faster.
f/2 will be a deal breaker for me, I need that extra stop, both for indoor light and bokeh
I'll mainly shoot stills and for video I can use the 18-55mm kit. It has silent linear motor.
I was thinking if getting XT2 will help me to keep up with my kid. Otherwise I'll have to get an entry level full frame dslr with a 50mm lens. Costs almost same of XT2, but I'd really hate to do that.