I don't really see how it will affect the economy, as most guilds are based on the skill itself & not how you make a profit of them. Obviously there might be a teleport to the Rune Essence mines close to a bank (possibly closer than the Magic Guild to the Yanille bank?) & place where you can buy/sell runes, who knows. That might change prices slightly, but I don't think that it will really upset the Grand Exchange.