Reading the answers to this post I think most of 'em failed to understand what OP is asking. He's not asking for a General Chat merge, or a PvP chat merge, or a "in-phase" Gen Chat merge.
There's a command in game which allows you to create a personal channel. E: /cjoin MyGuildName. This adds a channel on the /n being n any number from 4 to 9.
What OP is asking is making those Personal Channels work cross-factions, which is a good idea.