I noticed that none of the listed option selects against backdash seem to work against Chun (assuming I don’t screw them up.)
One of my personal favorites, which might be worth mention, is this:
meaty s.LK, buffer :qcf: :lp::hp::mk:
LK = thumb, lp = index, mk = middle, hp = pinky
If the LK whiffs because she backdashed, then the LK->MK target combo comes out and the MK part tags her if timed correctly (input done quickly). If LK hits or is blocked, special moves have input priority over the target combo, so EX Hayate comes out, pushing her to the corner to help prevent future backdashes. Unfortunately EX Hayate isn’t safe on block and she can super if she has it, or just jab you afterward most of the time. But the LK->MK target combo itself is also unsafe, so I find this worth doing regardless for the extra potential spacing reward.
You can also use EX Oroshi instead of EX Hayate if you don’t think she’ll jab you out of it, or do just MK + HP for a hayate feint if you don’t want to spend EX or feel like trying a karakusa tick throw. Other options that exist include plain oroshi or hayate, or buffering super with :qcf::qcf: :mk::hp: if you want to do that for some reason.
I know this method also works against El Fuerte and Ibuki’s backdashes. I’m not sure if there are any characters it doesn’t work on.
Makoto’s target combos are interesting for OS in general. It’s also possible to do something like delaying the MK so that it only comes out if LK hits/is blocked, then buffering something else immediately after the MK input which will come out if the LK whiffs. Something similar is possible with :r::mk:->:hk: target combo. Not sure of any practical uses atm.