I'm someone who doesn't like banging my head against a wall for too long, so I've been gearing up on my warlock before attempting Kanrethad properly, and I managed to get him down tonight after roughly an hour of attempts in 495 gear. I wouldn't say I was going super-crazy on the DPS, but I managed to finish the fight right after the second imp phase. If you have the gear to kill him within just one round of summons (give or take the imp phase - it's practically a buff as Destro anyway!), it's really not that hard a fight with practice.
By the end of the expansion even LFR players like me are probably going to be in 540 gear or more. By that point the boss will likely be dying within one cycle even without squeezing DPS with charge/chaos bolt combos. The fel hunters will probably be one-shottable, and even Kanrethad's chaos bolt should be survivable without cooldowns.
When you take all of that into account, I doubt we'll see any hard nerfs. As the gear level goes up most of the things that make the encounter hard will start to disappear, and nerfing the mechanics on top of that would just reduce it to a trivial level.
But anyway! I felt like I had to post in one of these threads now that I'm part of the green fire club. It felt super cool to pull off something that felt like a real challenge after not having raided since Wrath. I'd love more challenging solo stuff like this!