Multi-logging is a terrible idea to allow in the server. It hurts the economy immensely, lowing demand of items while at the same time increasing supply beyond need. Most players would rather have a mule account gather resources for their main account than go and buy it from other players, meaning that the game will take a huge sink in popularity for skillers. It will result in many usernames that were desirable to new players being taken up so that a player can have another 28 inventory spaces or another mindless drone fisherman.
It will hurt the great community we currently have. Players will be unable to tell who is a real player and who is just another slave account. Players will begin to become anti-social, depending on their other accounts rather than real players or themselves. You will lose players who disagree with multi-logging, and with them, potential donators that help the server. Those who already have helped by donating to the server may feel betrayed by such a controversial move.
Once and if the server begins to pick up more popularity with multi-logging allowed, the strain on the servers will increase. And with every player who is a potential donator now taking up multiple server slots instead of a single one, much more cash will be coming out of the developer's pocket to host the servers. Not to mention that the increased player count will attract more attention from Jagex and put the server more at risk of being shut down.
You may argue that if a player doesn't like multi-logging, then just don't do it. But how can we not? If we don't start multi-logging, the ones who do will soon be far ahead of us, constantly damaging the economy and hindering our ability to catch up to them. We may be able to afford to not multi-log for a while, but eventually it will come to a point for us to either pack up and leave the server or submit to the pressure.
Worst of all, allowing multi-logging will ruin the nostalgic feel of the game and RuneRebels will not be a true 2006 remake, and even your title will become false advertisement. If it is going to be kept, custom items and game mechanics might as well be added.
To the development team, all I can say is, I'm surprised at you.