Hi everyone, i stumbled upon this thread out of curiosity and after reading i thought i'd make an account and contribute to the discussion.
I've seen quite a few long winded inputs (the 360 motions are what i'm talking about), i've had the game for a little while now and considering i did not play SCIII or IV (did not like them) i don't know if my perspective can help you all that much.
However, i've managed to lock down my own method of performing CS regularly which didn't take me long at all to find, it's similar to some of the other posters 360 variants except mine is-
28284123666 B+G
However, during execution/buffering i break down the inputs for a couple of reasons i will explain later.
I play primarily on an Xbox 360 controller, i usually use a stick but i haven't felt compelled to use it yet since i get by fine on a pad.
2828- i input that pretty much like everyone else, however during some animations of certain moves i have a habit of centering my thumb on the d-pad and wiggling it up and down if i'm not sure i want to commit to the idea of a CS.
Once i decide to commit, i simply do a half circle forward motion (41236) a little before a move (any) has completed its animation and close the deal with 66 B+G.
I've had pretty much 95% success executing this move from any standard situation be it 2A/B, A/B/K, FC1/B or whatever.
The other reason i delay the input when buffering is because of the 666 B+G. If for instance (and this occurs a lot for me) i score a knockdown ie: 66+B, 66+A, WS A+B_A or similar, most of my opponents have the habit of rolling backwards on wide/infinite stages so i've got the move down to the point where i can RUN a specific distance and simply press B+G and complete my CS on their completed standing animation (although it will never be a iCS for me in this situation). It's almost as lenient in that sense as SCII's. You end your buffer with the 6 from 41236 so it causes Ivy to step, the moment it begins you should complete the second 6, this causes her to run. Watch her take a MAXIMUM of 1.5 steps (otherwise you lose the input window) and conclude with the last 6 & B+G commands.
As for iCS, i have completed that same input around i mentioned initially around 12 times so far (i've never intentionally gone for it except the first time i saw it in the command list and got my first one on my 7th attempt). I've not had much interest in testing it more since then but i hope what i've written might give someone a better idea about this moves application.
Apologies for the wall of text on my first post, please treat me kindly.