Kyoto Animation's next movie project is more Hibike! Euphonium. Presumably the movies will be canon because the author of the light novels is writing new books covering the same subjects.
Even if the movies aren't canon, it's really not a big deal -- just look at how great the K-On! movie was. I have a lot of faith in Kyoto Animation no matter what it puts its hands to.
The movies will come out in 2018 in Japan, so probably 2019 for the rest of us. But 2018 already has plenty of fun stuff scheduled, from the Winter Olympics to the World Cup, so saving something for 2019 works out fine.
Even with two more movies, it will be difficult for Hibike! to rise up any further in the ranks. Berserk, Scrapped Princess, Sora no Woto and Basilisk are no joke, and that's just the folks directly above Hibike! After that is stuff like Working!, Yuuki Yuuna, Shirobako -- I mean, it just gets more and more terrifying from there. But perhaps the two movies will help consolidate its position and make sure it doesn't drop any further down, so I won't say KyoAni's efforts are entirely in vain.