I would happily welcome cast times on the summons. Long cast times provide that feeling of build-up to something big coming; Fire IV and Midare come to mind. While instant casts are certainly convenient, it feels off for a supposed caster to have less cast times than a Samurai. Not to mention that SMN doesn't really have much to play around with mechanically, at least more casts than Ruby Rite and Slipstream to work around provides some kind of mechanic to plan around.

Call me crazy, but I kinda want cast times on Bard songs as well, it just feels more fitting for the bard to feel like it has to play a melody for its effects rather than strum a chord.