why not put unwhitelisted players in a special dimension?

[joeyjumper94]

while in spectator mode, someone could go around and find things unfairly
they could clip into the ground and xray for stuff like buried chests

[CaptainRexPL]

Some low-end servers might have problem with handling another dimension so I don't think that this solution would be perfect for all servers. Also, this mod is supposed to protect servers from griefers so I guess that you can't really do much when you're in spectator mode.
On the other hand, if this mod would only freeze the player they would still be able to use stuff like freecam so this would not be a perfect solution either.

[joeyjumper94]

oh idea, what if unwhitelisted players had their clients told that there were no blocks. so all that they could see is an empty world with nothing