In order for the game to synchronize an action -- say, taking a step in one direction -- it must send data to all connected clients whenever that action takes place. Those clients, in turn, must be "listening" for that data and must respond to it appropriately -- say, by updating the other players' OWs on-screen -- when it is received.
This must be done for everything that is synchronized. If you need to synchronize wild battles, then the games must be coded to send, check for, and respond to data packets when they are initiated. Movement, trainer battles, random OW movements -- same thing.
Essentially, you'd literally have to hack nearly every facet of the game engine and modify them to make them sync. Failure to hack even one system -- the random movement of NPC OWs, for example -- can lead to massive desyncs in the manner I have described earlier in this thread.
And an auto-connect system like you're describing would require even more work -- constantly listening and broadcasting for additional connections, and synching several connections at a time... Having to spawn new OWs and sync new data at any moment, should a player come within range of the Wireless Adapter... All of this, as opposed to a direct one-to-one connection between two and only two players, initiated with a specific trigger (i.e. talking to an NPC to start a link) and deactivated with another specific trigger.