Ragnar - That low-level player can bypass that scenario by phasing to another PVP server, or PVE-Only server. They can't gank you if it's not allowed.
If there is a lot less people to group in PVE, that means there would be a significant amount of people that would prefer to play on PVP server. I don't believe that is the case, but if the Megaserver is doing it's job, there will still be a solid population on your server.
For guilds that are PVP-based, this will provide variety.
For guilds that are PVE-based, nothing has changed.