Yes, there are addons that can filter, but why not just keep guild ads out of world from the jump? Guild ads are just macros that people can click every ten seconds for eternity; sure there's an argument of "what about LFM", but those ads die eventually. And let's face it, if people are looking for a guild they aren't looking in /world. There's LFG, there's organic interaction in PUGs and there are guild recruitment channels in Discord.
There's a chance to keep /world interesting and not let it get taken over by guild spammers.