I don't think this is a very good idea. The strength of two 6x reincarnated legendary characters is so absurdly strong, I feel like exploring damn near all zones is possible with the right combination of characters. Not that I'm doubting anyone's skill, but controlling four players can get exhausting, which leads to players looking for easier ways to do so. I believe this would eventually turn into botting and that's something the staff frowns upon greatly.
It's nothing to to with the strength, but the speed. I explored all of Shadow among others alone, and could do the same for almost anywhere.
There are people I don't want to play with. There are people who don't want to play with me. Etc etc etc. That's not going to change as the playerbase dwindles. It's more of a hindrance bringing people than not, most of the time.
It's going to get to a point where I know that, for me, the game will end because the people I enjoy playing with aren't playing or available when I am. I'll likely just do it regardless and, if I'm stopped, I was going to stop anyway🤷