Doesn’t need an experiment. Other games use it and it works. We already know what happens. It just works, with caveats.
The caveats are that people who get raided will sometimes log off during a raid and hopes the timer kicks in before the raiders get too far. If the raiders are competent enough, or the defenders didn’t build enough, it doesn’t work. And sometimes people wait for stronger clans/guilds/units/etc to log off and then use the window to raid as far as they can.
Those aren’t theories. Those are experiences I’ve had. And in my opinion, they aren’t as bad as missing a 5 hour window and losing what a raider can take in 5 hours of uncontested mayhem.
Now should Funcom Provided Servers do this setting? I can’t really answer that. That’s up to them. Those who like to offline with impunity will lose the ability to do so. That will upset those players. Depends on if Funcom is willing to do that over appeasing those who support the change. Or simply wish to leave things be as they always have been.