I think there should be a warning to not enable this because of falses without reporting it

What are you talking about? I don't quite understand what you're trying to say. This does not cause falses (if anything it would hide falses assuming they exist, which for reach is just not true). This just skips reach check if the target is not a player.

What are you talking about? I don't quite understand what you're trying to say. This does not cause falses (if anything it would hide falses assuming they exist, which for reach is just not true). This just skips reach check if the target is not a player.

reach falses on non-player entity -> this gets enabled -> false never gets reported -> false never gets fixed

What are you talking about? I don't quite understand what you're trying to say. This does not cause falses (if anything it would hide falses assuming they exist, which for reach is just not true). This just skips reach check if the target is not a player.

reach falses on non-player entity -> this gets enabled -> false never gets reported -> false never gets fixed

There are already false positives involving Reach with entities that are not Players. In version 1.8, at least, I was able to reproduce false positives involving Horse, Elder Guardian, and Skeleton.