To be honest, I was planning on it, as I have been happy with its performance still, and suspect iOS 10 won't cause too much trouble (plenty of other A8 devices in Apple's lineup). Still, I'm very tempted to pick up an SE, as I'm a fan of the form factor and wouldn't mind the little speed boost and better rear camera. Plus, I can resell my 6 and mostly cover the price.
The other big question mark is what happens in the fall: does the 6 become "free" on contract ($449) and is sold alongside the SE ($399), or is it discontinued? That would leave the lineup being the SE, 6s, and whatever the new model is...pretty nice. Unfortunately, being discontinued and slightly-less-powerful-than-all-the-current-models would hurt the 6's resale at that time, so I'm sort of betting September goes that way by selling my 6 now.
Still, bottom line is that if you aren't in the market for a new phone, the 6 really should be good for quite awhile - Apple still supports plenty of older devices on the current OS, and only the 4S feels really sluggish (I have a 5c that's become a media streamer).