Virtual realms act sort of like how battlegroups act for PvP except on a wider scale. If four roleplay realms are a part of the same virtual realm, players from the newly created virtual realm will be able to join guilds together, run raids together, use the same auction house, and form arena teams.
This is going to be a huge, game changing thing for World of Warcraft. There are a ton of low population servers that are losing their player bases due to realm transfers. This will ensure that these players can still participate in lively communities, have healthy guild lives, etc. without having to drop the $25 to transfer.
I am super excited to see what sort of changes this will bring. I am hoping the transfer goes smoothly for my realm, Wyrmrest Accord. We have our own lively culture separate from other RP realms, but it will be interesting to see how it ultimately turns out come WoW 5.4.
