I've been doing some testing and noticed that CS lasts noticeably longer this expansion. While it still claims a 6s duration, the actual time between when you cast a CS and the debuff falling is consistently 6.5s. Since ability queuing was also fixed this expansion(to allow you to queue abilities when they're on CD to trigger when the CD ends and GCD is available), it's possible to fully make use of that time period with any combination of abilities.
With regards to Arms specifically, a 6.5s window after using CS to fit abilities into allows a slightly higher damage rotation. 1.5s of the window is spent waiting on CS's GCD, leaving 5s to work with. The last ability landing at the end of that 5s time period can have any length GCD, since that time will be spent waiting outside the CS window rather than inside it. The best use of that 5s of GCD time will be 2 OPs and 3 of MS/CS/Slam. 2*1s + 2*1.5s = using the full 5s available, with the last GCD being an MS/CS/Slam landing just as the debuff is about to expire. Using one more OP during CS will force you to give up a MS/CS/Slam(all of which do more damage) inside the window, which isn't desirable. Using 2 less OPs gains you only 1 extra Slam, which deals less damage than 2 OPs(unless well over OP's crit cap), again not desirable.
This leads to 3 ways the CS rotation can work out, depending on the time until MS comes off CD when you hit CS:
CS MS OP OP Slam MS
CS OP MS OP Slam (Slam/CS)
CS OP OP MS Slam (Slam/CS)
In all of those cases, 2 OPs and 3 full GCDs fit inside the CS window, which works extremely reliably, flexibly, and can be worked in seamlessly with a normal rotation. Replacing OPs with Slams will leave you with extra TfB stacks after CS ends, which can just be burned off with MS OP OP OP cycles as needed. However, too many back to back CSs caused by sudden death procs can result in wasted OPs. To avoid that, the slam as the second to last GCD in every cycle should be OP instead if you have 3+ stacks of TfB at that point in time. You'll get less damage out of the CS, but wasting OP chances(and therefore MS uses over time as well) is a greater cost.
A example rotation would look like the one below. {} = CS window, * = SD proc at around this GCD, numbers above line = TfB stacks after that GCD:
2 1 0 2 1 3 2 1 3 2 1 3 2 1 3 2 4 3 2 4 3 2 4 3 2 4 3 2 1 3 2 1 0
MS CS {OP OP MS SL SL} OP MS OP OP* CS {MS OP OP SL MS} OP* CS {OP MS OP* SL CS} {MS OP OP SL* MS} CS {OP OP MS OP SL} OP MS OP OP OP MS OP OP OP
This is obviously just a 100-20% rotation, since Execute is significantly higher DPR/DPE than Slam, which changes things. DR can be dropped in anywhere you're not hitting MS (ideally outside a CS and along with BB). With the crit of T15 4pc active, trying to do MS SL SL SL inside a CS window will probably be more effective, but I haven't done any modeling of that yet.