Keeping zen sphere on CD is not allways a dps gain. Using energizing brew on CD is allmost allways a waste since you really need to have low energy and no procs to make full use, so wasting it at a time where you're active versus delaying it for a time where you need something to cast is a real waste.
As for ChiBrew, as all spells who stack up to two times, you just need to avoid ever capping 2 stacks of it and use them before the fight ends to make optimal use of it. Its really not hard to use ChiBrew optimally.
As for CX and Serenity, I think they play very differently indeed.
You're probably thinking that the whole Jab, RSK, FoF rotation + TEB is way more important than those two talents are, and you're not wrong.
However, most specs in the game play with very few spells in their rotation, yet are not defined by those spells but by something extremely different. Frost DK's can, at times, be played with two main spells (frost strike and howling blast) with very little dps loss. I'm exagerating a bit, and using obliterate at the right time is a dps gain, plus necrotic plague isn't optimal as far as lvl 100 is concerned. However, you can macro your pillar of frost into frost strike, bind howling blast on the rest of your keyboard and do decently. There is quite some skill though in the spec, mainly in optimizing your rune regeneration, when to dump Runic Power, when to use empower weapon and how to use AMS (thats actually a huge part of frost DK ST skill).
We got many more spells to use in our rotation, no matter which talents we go for, yet I feel like there is a huge difference between serenity and CX. Ofc I have my monk reflexes, but it really feels quite different. There is quite a lot to change depending on both playstyles.
I'm expecting several Monks to remain ChiExplosion alltimers after the buff. I know the gap will increase, but I think the benefits are still the same. Some players flat out prefer the playstyle, most bosses have some small cleave at some point (only zakuun makes a noticeable exception this tier), then there is the benefits of never needing to delay a spell for ring usage, benefiting from bloodlust burstphases (aka when the raid needs it) without delaying anything, having some range (aka less downtime), and above all having one set of optimal enchants/gems for all bosses.
I'm not saying CX is better than serenity overall. I'm just saying that the things that got people to play CX all time are still true, that the spec only got buffed, so if it works, no need to fix it. Raitank proved us that WW could be one of the best dps's in the game going CX all time for all 13 bosses, so with a buff this is only truer. Yes, serenity might be better come 6.2.2 for ST, but the things that got people to play CX was not a 7:30 minutes patchwerk fight with no delay, it was other concerns. A 2% increased difference (BoK buff really only widens the gap by a further 2%, which is relevant but fine) has nothing to do with their decision.
I for one will probably keep going CX all time. I've kept gemming for multistrike atm since I'm doing mythic Gorefiend and am not allowed to cleave passively, but I think the spec kept its perks.
Still excited to see those buffs next wednesday. I didn't expect us to get such buffs, don't think it will put us in a spot where we're blatantly OP as arms/DWF were at the begining of the patch. However, we'll be able to compete on with allmost every spec for ST and will be very strong in any cleave situation. The results will be pretty insane.
I'm happy to that BrewMaster is seing some love too (tiger palm getting 20% is really a BrM specific buff). I've been asked to offtank at times, and my experience of it this tier is "bring as many dps trinkets as you can in your bags". I've been running SDI+Soul Kappacitor, some BHotM on M gorefiend, I'd use MotB if I had one... In a greedy tank environement, it felt pretty bad doing lower dps than other tank and therefore being assigned all mechanics to allow the other tank to grind more. This will help make things more even.