They are not exactly hard to fake in LuxCore too:
with the not so small difference that they are true caustics instead of faked one.
To further elaborate: the paper makes sense in the context if this infinite angle reduction ... in practice it may be different, I can try that.
Nope but it would be useless because the same paths are better rendered by normal path tracing.
Yes, they are just added together.
It should be more a Metropolis problem than PSR (may be accentuated by the very narrow angles used by PSR).