When I talked about "20 years ago" I talked about the design with AC power just rectified and fed to long LED chains - not the use of two capacitors with reversed polarity.

Some capacitors (not all) can survive the polarity reversal as long as the polarity isn't permanently reversed. They fail quickly if they have a reversed DC potential. But they can handle AC because there will be current on both directions that protects the barrier from being reducted. Using two capacitors with reversed polarity is just to make the design symmetrical. If ignoring the symmetry, you could use a single capacitor.

But no - this is not a design to use. It's not all polarized capacitors that only fails for reversed DC but survives AC. And even when using a cap that survives AC, the capacitor is still used outside the manufacturer specification, which means that rated ageing, usage temperatures, ripple current etc do not apply anymore. When people do need a capacitor for AC, they should get a non-polarized capacitor.